REVIEW ARTICLE published: 05 February 2015 doi: 10.3389/fphar.2015.00006 Interactions of the opioid and cannabinoid systems in reward: Insights from knockout studies

Katia Befort* CNRS, Laboratoire de Neurosciences Cognitives et Adaptatives – UMR7364, Faculté de Psychologie, Neuropôle de Strasbourg – Université de Strasbourg, Strasbourg, France

Edited by: The opioid system consists of three receptors, mu, delta, and kappa, which are Dominique Massotte, Institut des activated by endogenous opioid peptides (enkephalins, endorphins, and dynorphins). The Neurosciences Cellulaires et Intégratives, France endogenous cannabinoid system comprises lipid neuromodulators (endocannabinoids), enzymes for their synthesis and their degradation and two well-characterized receptors, Reviewed by: Fernando Berrendero, Universitat cannabinoid receptors CB1 and CB2. These systems play a major role in the control of Pompeu Fabra, Spain pain as well as in mood regulation, reward processing and the development of addiction. Krisztina Monory, University Medical Both opioid and cannabinoid receptors are coupled to G proteins and are expressed Centre of the Johannes Gutenberg University, Germany throughout the brain reinforcement circuitry. Extending classical pharmacology, research using genetically modified mice has provided important progress in the identification of the *Correspondence: Katia Befort, CNRS, Laboratoire de specific contribution of each component of these endogenous systems in vivo on reward Neurosciences Cognitives et process. This review will summarize available genetic tools and our present knowledge on Adaptatives – UMR7364, Faculté de the consequences of gene knockout on reinforced behaviors in both systems, with a focus Psychologie, Neuropôle de Strasbourg – Université de on their potential interactions. A better understanding of opioid–cannabinoid interactions Strasbourg, 12, rue Goethe, F -67000 may provide novel strategies for therapies in addicted individuals. Strasbourg, France Keywords: opioid, cannabinoid, G protein-coupled receptors, reward, genetically modified mice e-mail: [email protected]

INTRODUCTION Among illicit drugs, opiate and cannabinoid derivatives are Drug abuse often leads to a complex pharmaco-dependent state highly abused in Europe. Morphine-like opiates are powerful which is defined by the term addiction. Addiction is consid- analgesics and currently represent the major therapeutic reme- ered as a neuropsychiatric disease. It develops from an initial dies for the treatment of severe pain. They are also abused recreational drug use, evolves toward compulsive drug-seeking for their recreational euphoric effects. In Europe, 1.3 million behavior and excessive drug-intake with the appearance of nega- people are addicted to heroin, the primary drug for which tive emotional states such as anxiety or irritability when the drug treatment requests are sought. Cannabis is the most worldwide is not accessible, and uncontrolled intake reaching a stage where consumed drug of abuse, with THC being the most abun- the drug interferes with daily activities, despite the emergence dant active constituent found in the various preparations of of adverse consequences (Leshner, 1997; Everitt and Robbins, the drug. More than 73 million European citizens have used 2005; Robinson and Berridge, 2008; Koob, 2009). This patholog- cannabis in the last year and it is estimated that about 7% of ical process develops in 15–30% of casual drug users and several cannabis users has become dependent on this drug. There is also factors may explain individual’s vulnerability to addiction, includ- a high prevalence of users who seek treatment for dependence on ing genetic, psychological and environmental factors (Swendsen it (http://www.emcdda.europa.eu/publications/edr/trends-develo and Le Moal, 2011; Belin and Deroche-Gamonet, 2012; Pattij pments/2014). Interestingly, new derivatives of these abused drugs and De Vries, 2013; Saunders and Robinson, 2013). Addiction are invading the market, notably through internet. Fentanyl is a major threat to public health and represents a societal prob- derivatives as new opioid drugs and synthetic cannabimimetics, lem especially in developed countries and the economic cost it also known as “spices,” are becoming more and more popular entails (investments in research, treatment and prevention) is (Fattore and Fratta, 2011). These abusive substances interact with considerable (Gustavsson et al., 2011). two neuromodulator sytems, the opioid and the endocannabinoid systems. Abbreviations: 2-AG, 2-arachidonoylglycerol; AEA, anandamide, N-arachidonoyl- ethanolamide; CB1, type 1 cannabinoid receptor; CB2, type 2 cannabi- THE OPIOID SYSTEM noid receptor; cKO, conditional knockout mice; CPA, conditioned place The opioid system consists of endogenous opioid peptides aversion; CP 55,940, (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]- (enkephalins, endorphins, and dynorphins) from precursors 4-(3-hydroxypropyl)cyclohexan-1-ol; CPP, conditioned place preference; CPu, caudate putamen; DA, dopamine; DAGL, diacylglycerol lipase; FAAH, (Penk, Pdyn, and Pomc) which activate three opioid receptors, fatty acid amide hydrolase; G protein, guanine nucleotide binding pro- namely mu, delta, and kappa (Kieffer, 1995). The three mem- tein; GABA, c-aminobutyric acid; GPCR, G protein coupled receptor; brane receptors, cloned in the early nineties (Evans et al., 1992; KO, knockout; MGL, monoacylglycerol lipase; NAPE-PLD, N-acyl phos- Kieffer et al., 1992; Simonin et al., 1994, 1995; Mestek et al., 1995) phatidylethanolamine phospholipase D; THC, Delta-9-tetrahydrocannabinol; WIN 55,212-2, 2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]- are GPCR with coupling to Gi/Go proteins, of which the 3D 1,4-benzoxazin-yl-1-naphtalenylmethanone mesylate; WT, wild-type. structure was recently resolved (see Filizola and Devi, 2014).

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Opioid receptors and endogenous opioid peptides are largely energy balance, modulation of pain response, with processing of expressed throughout the nervous system, noticeably within areas central and peripheral pain signals, learning and memory, reward of the neurocircuitry of addiction associated with reward, motiva- and emotions. It has also been shown to be involved in neuroge- tion, or learning and stress (Mansour et al., 1995; Le Merrer et al., nesis and would play a neuroprotective role in some pathological 2009; Koob and Volkow, 2010; Erbs et al., 2014). Besides its key conditions (for recent reviews see Gardner, 2005; Solinas et al., role in many aspects of addition (Lutz and Kieffer, 2013a), the 2008; Maldonado et al., 2011; Zanettini et al., 2011; Panagis et al., opioid system also plays a part in a diverse range of physiological 2014; Piomelli, 2014). Distribution of the two receptors in the functions including nociception, mood control, eating behavior, central and peripheral system is rather different (Pertwee, 2010). or cognitive processes (Contet et al., 2004; Pradhan et al., 2011; Indeed, CB1 is highly abundant in the central nervous system in Stein, 2013; Bodnar, 2014; Nogueiras et al., 2014). areas involved in reward, regulation of appetite and nociception (see Figure 1) while CB2 was initially described as a peripheral THE ENDOCANNABINOID SYSTEM receptor (Maldonado et al., 2006, 2011; Mackie, 2008). Recent The endocannabinoid system is a neuromodulatory system con- studies have proposed a low but significant expression of this sisting of two well characterized transmembrane receptors coupled receptor in several brain structures including striatum, hippocam- to G protein (Gi/Go), CB1, and CB2 cloned in the 1990’s (Mat- pus, and thalamus (Wotherspoon et al., 2005; Gong et al., 2006; suda et al., 1990; Munro et al., 1993). The endogenous ligands Onaivi et al., 2006) and more recently into ventral tegmental area are lipid neuromodulators, the main ones being AEA and 2-AG. neurons (Zhang et al., 2014). Only few data are therefore available Both are synthesized from phospholipid precursors and act locally for the CB2 receptor in central function but growing evidence sug- as retrograde regulators of synaptic transmission throughout the gest a role in addictive processes, with an implication in cocaine, central nervous system. These lipids are released by postsynaptic nicotine, or ethanol effects (Xi et al., 2011; Ignatowska-Jankowska neurons and mainly activate presynaptic cannabinoid receptors to et al., 2013; Navarrete et al., 2013; Ortega-Alvaro et al., 2013). To transiently or persistently suppress transmitter release from both our knowledge, no data is available thus far concerning a potential excitatory and inhibitory synapses (recently reviewed in Ohno- role of CB2 in opioid mediated responses. Interestingly, other Shosaku and Kano, 2014). Multiple pathways are involved in AEA non-CB1 and non-CB2 receptors have been proposed to interact biosynthesis with several still not fully characterized enzymes. with endocannabinoids like the orphan GPCR GPR55 or a channel AEA can be generated from the membrane phospholipid precur- vanilloid TRPV1 recognizing capsaicin. These interactions could sor N-arachidonoyl phosphatidylethalonamine (NAPE) through a potentially explain some pharmacology of cannabis that cannot two-step process with first a calcium-dependent transacylase fol- be accounted for by CB1 and CB2 activation, but further studies lowed by a phospholipase D (NAPE-PLD) hydrolysis (Liu et al., using KO approaches may help to provide a better understanding 2008). Phospholipase C (PLC) and DAGL are involved in 2-AG of this pharmacology (De Petrocellis and Di Marzo, 2010). synthesis (Ahn et al., 2008). Their degradation is conducted by two specific enzymatic systems, the FAAH (Cravatt et al., 1996) CROSS TALK BETWEEN THESE NEUROTRANSMITTER SYSTEMS and the MGL (Dinh et al., 2002), for AEA and 2-AG, respectively Many neurotransmitter systems are involved when addiction (Ahn et al., 2008). The endocannabinoid system plays a key role in develops, and both opioid and endocannabinoid systems are

FIGURE 1 | Schematic representation of the distribution of mu opioid (one), moderate (two), and high (three) expression levels (adapted from and CB1 cannabinoid receptors in the central nervous system. CB1 Mackie, 2005; Erbs et al., 2014 and references therein). Amb, ambiguous receptor distribution over the whole central nervous system is indicated by nucleus; BLA, basolateral amygdala; CeA, central amygdala; CPu, caudate circle shapes with low (white), moderate (gray) and high (dark gray) putamen; DB, diagonal band; DRN, dorsal raphe nucleus; GP,globus pallidus; expression. Major localization of CB1 receptor (mRNA and protein) is in Hyp, hypothalamus; LC, locus coeruleus; LHb, lateral habenular nucleus; cortical areas, amygdala, striatum, and cerebellum. Moderate and low mHb, medial habenular nucleus; NAc, nucleus accumbens; OB, olfactory expression levels are observed in thalamic, hypothalamic, and brainstem bulb; PAG, periaqueductal gray; SNr, substantia nigra pars reticulate; Sol, regions. Interestingly, the mu opioid receptor is also expressed in these CB1 nucleus of the solitary tract; STh, subthalamic nucleus (ventral thalamus); Th, expressing brain areas but at various levels, indicated by diamonds for low dorsal thalamus; Tu, olfactory tubercle; VTA, ventral tegmental area.

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major players in addictive disorders. In addition to their spe- as extinction (response rate when drug-delivery has stopped) cific ligands, both systems have also been implicated in the action and reinstatement induced by cues, context or stress (relapse mechanism of several other addictive drugs, like ethanol, nico- to drug-seeking) which will reflect aspects of excessive con- tine, or psychostimulants. Although the endocannabinoid system sumption (Sanchis-Segura and Spanagel, 2006). Intravenous SA has been known to interact with other systems like hypocre- has been extensively developed for opiates but more difficult tin, dopaminergic, and adenosinergic systems (Fernandez-Ruiz to establish for cannabinoid compounds. Adaptations includ- et al., 2010; Ferre et al., 2010; Tebano et al., 2012), its interac- ing drug priming, low doses, food restriction, animal restraint, tion with the opioid system is now well established (Fattore or use of various cannabinoid agonists were often necessary et al., 2005; Vigano et al., 2005; Robledo et al., 2008; Trigo et al., (Maldonado, 2002; Panlilio et al., 2010; Panagis et al., 2014). Nev- 2010). These two systems share neuroanatomical, neurochemi- ertheless, iv SA of both THC and the synthetic cannabinoid cal, and pharmacological, characteristics, this phenomenon is yet WIN55,212-2 have been successfully described both in rats and less well documented for the CB2 receptor. Figure 1 illustrates mice, and extended to the study of KO mice (Martellotta et al., brain structures expressing CB1 receptors and depicts expres- 1998; Fattore et al., 2001; Mendizabal et al., 2006; Flores et al., sion level of mu opioid receptors in these areas. The existence 2014). A very recent study demonstrated for the first time that of a specific opioid–cannabinoid interaction in the modula- 2-AG is self-administered by rats and stimulates DA transmission tion of neurochemical effects as well as behavioral responses (De Luca et al., 2014). associated with reward and relapse have been demonstrated In addition, a well-accepted model to study the reinforcement by pharmacological and genetic approaches but experimental properties of abused drugs is the CPP which is a non-operant results remain controversial (Manzanares et al., 1999; Fattore et al., paradigm. The reinforcing properties are associated with environ- 2005; Maldonado et al., 2011). Furthermore, molecular interac- mental stimuli (cues), such as the context in which the drug is tions between receptors have been shown with colocalization or administered. If the drug or a combination of drugs is aversive, heterodimerization data mainly for CB1 and delta or mu opioid animals avoid the drug-paired compartment (CPA) (Tzschentke, receptors within spinal cord, striatum, or locus coeruleus. This 2007). These paradigms have been widely used to study opiates phenomenon may also account for specific responses at the cel- or cannabinoids effects in mutant mice. However, data reporting lular level (Scavone et al., 2013; Massotte, 2014). However, the reinforcing properties for THC and other cannabinoids are rather physiological effects of these molecular interactions have had yet controversial with a critical concern about experimental condi- to be revealed. tions, with dose or injection schedule as major parameters to reveal either positive CPP or negative CPA properties of cannabinoids AIM OF THE REVIEW (Panagis et al., 2014). Pharmacological evidence for cross-talk with the synergetic effect On top of these two main paradigms (SA and CPP) other tasks of opioid and cannabinoid ligands in many functions related to have been developed like intracranial self-stimulation (ICSS) as addiction (mood, stress, learning process ...) have been revealed a model to measure reward-facilitating effect of an abused sub- and here we will review the implications of both systems regard- stance although it is rather difficult to set up in mice and therefore ing reward aspects. As several reviews have recently reported about little data is available (Panagis et al., 2014). Furthermore, with- these interactions (see above), we will focus our interest only on drawal signs appear after cessation of chronic drug exposure, genetic studies using KO mice. We will first present the available either spontaneously or precipitated by an antagonist treatment, genetic tools for both systems. We will then provide an update of and these signs can be scored for providing an index of depen- results on reinforced behaviors to highlight insights into the par- dence (Maldonado et al., 1996). In order to make a meaningful ticular role of the opioid system in responses to cannabinoids and comparison in the evaluation of the specific involvement of com- the endocannabinoid system in responses to prototypical opiates ponents of opioid or cannabinoid systems in reward process, it like morphine. We will summarize the behavioral responses of KO is crucial to compare, when possible, the different mutant lines mice to these drugs and propose a role for the potential interaction with their WT littermates in the exact same procedure to avoid of these two endogenous systems in addictive processes. bias from technical or experimental variations. Interestingly, such direct comparison has been recently performed for the four com- REWARD MEASURES IN MICE ponents of the opioid system (mu, delta, Penk, and Pdyn) to Opioid and cannabinoid derivatives induce dependence. To study demonstrate differential behavior in the acquisition and relapse rewarding effects mediated by specific brain circuits in preclin- of cocaine SA in the four mutant mice (Gutierrez-Cuesta et al., ical research, several behavioral models have been developed 2014). in rodents. The most reliable model to evaluate the reinforc- ing properties of a psychoactive compound in rodents is the GENERATION OF DEFICIENT MICE IN REGARDS TO self-administration (SA) paradigm which is based on a volun- COMPONENTS OF THE OPIOID OR CANNABINOID SYSTEMS tary procedure to obtain the drug, coupled with the association For each component of the opioid and the cannabinoid systems, of a signal (Panlilio and Goldberg, 2007). This operant sys- various lines of genetically modified mice have been generated. tem allows measuring both rewarding as well as motivational Table 1 presents a list for conventional KO mouse lines that have effects of an abused drug. Several aspect of addictive behav- been described so far. The original papers describing the develop- iors can be evaluated with this paradigm, with acquisition (fixed ment of the constitutive deletion are presented with the targeted ratio) and motivation (progressive ratio) for the drug as well area of the suppressed gene.

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Table 1 | Knockout mouse lines for the opioid and the cannabinoid Table 1 | Continued systems. Gene knockout Targeted exon Reference Gene knockout Targeted exon Reference DAGLalpha Exon 1 Gao et al. (2010) Opioid system Exons 3 and 4 Tanimura et al. (2010) Oprm Exon 2 Matthes et al. (1996) Intron 4-Exon 1(gene Yoshino et al. (2011) Exon 1 Sora et al. (2001) trapping) Exon 1 Tian et al. (1997) DAGLbeta Exon 1 Gao et al. (2010) Exons 2 and 3 Loh et al. (1998) Exons 10 and 11 Tanimura et al. (2010) Exon 1 Schuller et al. (1999) Exon 1 (gene Yoshino et al. (2011) Exons 2 and 3 van Rijn and Whistler (2009) trapping) Exon 11 (splice Pan et al. (2009) cnr1/cnr2 Jarai et al. (1999) variant) FAAH/cnr1 Sun et al. (2009) Oprd Exon 2 Zhu et al. (1999) Exon 1 Filliol et al. (2000) FAAH/cnr2 Sun et al. (2009) Exon 2 van Rijn and Whistler (2009) FAAH/cnr1 Wise et al. (2007) Oprk Exon 1 Simonin et al. (1998) This table summarizes the published report of KO mouse lines for the different Exon 3 Hough et al. (2000) partners of these two systems and combinatorial lines, with the original papers as reference. The area of the gene that has been targeted is indicated. Exon 3 Ansonoff et al. (2006)

Exon 2 van Rijn and Whistler (2009) THE OPIOID SYSTEM Exon 3 Van’t Veer et al. (2013) For components of the opioid system, the mu receptor drew the Oprm/oprd Simonin et al. (2001) most attention with the description of six distinct genetically mod- Oprm/oprd/oprk Simonin et al. (2001) ified lines targeting the coding regions of the oprm gene, with Clarke et al. (2002) either exon 1, exon 2 or both exons 2 and 3 targeted for the dele- tion (Matthes et al.,1996; Tian et al.,1997; Loh et al.,1998; Schuller Penk Exon 3 Konig et al. (1996) et al., 1999; Sora et al., 2001; Pan et al., 2009; van Rijn and Whistler, Exon 3 Ragnauth et al. (2001) 2009). Interestingly, the mu opioid receptor KO mice allowed to Pdyn Exon 3 Sharifi et al. (2001) unambiguously demonstrate that the mu receptor was the molec- Exon 3 Zimmer et al. (2001) ular target for morphine, the prototype of opiate ligand widely Exon 3 Loacker et al. (2007) used in clinics for its therapeutic effect in pain relief. Morphine had Pomc Exon 3 Rubinstein et al. (1996) neither analgesic effects nor rewarding properties in these mutant Exon 3 Yaswen et al. (1999) mice (for reviews, see Contet et al., 2004; Gaveriaux-Ruff, 2013). An additional mutant line was constructed which targeted exon Penk/Pdyn Clarke et al. (2003) 11, a splice variant for the mu receptor, located upstream of exon Cannabinoid system 1. In these deficient mice, a 25% decrease of receptor expression Cnr1 Exon 2 Zimmer et al. (1999) was observed (Pan et al., 2009), leading to difficult interpretation Exon 2 Ledent et al. (1999) of the KO effect on opiate pharmacology (Gaveriaux-Ruff, 2013). Exon 2 Marsicano et al. (2002) For deletion of the delta receptor, either exon 1 or 2 were tar- Exon 2 Robbe et al. (2002) getedintheoprd gene (Zhu et al., 1999; Filliol et al., 2000; van Rijn and Whistler, 2009). These mice were characterized for behavioral Cnr2 Exon 2 Jarai et al. (1999), Buckley responses related to mood and analgesia, but the contribution of et al. (2000) delta receptor in reward processes was less clear (Pradhan et al., Exon 2 Wotherspoon et al. (2005) 2011; Charbogne et al., 2014). Five distinct constructions have FAAH Exon 1 Cravatt et al. (2001) been reported targeting either exon 1, 2, or 3 of the oprk gene to MGL Exon 3 Uchigashima et al. (2011) obtain KO mice for the kappa opioid receptor (Simonin et al.,1998; Exons 3 and 4 Taschler et al. (2011) Hough et al., 2000; Ansonoff et al., 2006; van Rijn and Whistler, 2009; Van’t Veer et al., 2013). The two most recent mutants were Intron 3–exon 4 Schlosburg et al. (2010) strategically obtained in order to generate a parallel conditional (gene trapping) KO mice (see below) using a Cre-lox approach, with targeted Exons 1 and 2 Chanda et al. (2010) exons floxed with loxP sites. The mutation impaired pharma- NAPE-PLD Exon 4 Leung et al. (2006) cological actions of the selective kappa-agonist U-50,488H, and Exon 3 Tsuboi et al. (2011) revealed a tonic implication of kappa receptors in the perception of visceral pain. Morphine-CPP was unchanged, but both mor- (Continued) phine withdrawal signs as well as emotional responses during

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opiate abstinence were reduced (Simonin et al., 1998; Lutz et al., (Frazier, 2011). The endocannabinoid system is characterized by 2014), suggesting an anti-reward role for kappa receptors. a rapid catabolism of the endogenous ligands. Among the degrad- Mice with deleted opioid peptide precursors were also gener- ing enzymes of endocannabinoids, FAAH is the major enzyme ated. For proopiomelanocortin (Pomc), two lines were produced, responsible for the degradation of AEA and one KO line was gen- one specifically deleting βendorphin (Rubinstein et al.,1996) while erated targeting exon 1 of the Faah gene (Cravatt et al., 2001). the second was targeting the whole coding region, deleting both These mutant mice exhibited more than 15-fold higher brain levels opioid and non-opioid active petides (Yaswen et al., 1999). KO of AEA than WT animals and displayed reduced pain sensitivity. mice for Penk gene were generated by two distinct laboratories, The major degrading enzyme of the endocannabinoid 2-AG is both leading to deletion of the 5 partofexon3(Konig et al., 1996; MGL and four KO lines were generated. Three KO lines target- Ragnauth et al., 2001). For deleting dynorphin in mutant animals, ing mgll gene exons 1 and 2 (Chanda et al., 2010), exon 3, or exons3and4(Sharifi et al., 2001)orexon3withapartofexon4 exons 3 and 4 were recently generated with a Cre/lox approach (Zimmer et al., 2001) of the Pdyn gene were targeted. Data from (Taschler et al., 2011; Uchigashima et al., 2011). Another line was peptide KO mice in regards to opiate rewarding effect were more obtained by gene trapping technology (Texas Institute of Genomic complex. The βendorphin KO mice showed increased (Skoubis Medicine) with a gene trap cassette inserted into the mgll intron 3, et al., 2005) or unchanged (Niikura et al., 2008) morphine-CPP upstream of the catalytic exon 4 (Schlosburg et al., 2010). Genetic depending on the dose and paradigm used and it was invariable deletion of MGL leads to alteration in endocannabinoid signal- both in mice lacking Penk (Skoubis et al., 2005)orPdyn(Zimmer ing with increased brain 2-AG levels by ∼10-fold. These animals et al., 2001; Mizoguchi et al., 2010). were mainly characterized by behavioral consequences of the gene deletion for pain perception (Schlosburg et al., 2010; Uchigashima THE CANNABINOID SYSTEM et al., 2011; Petrenko et al., 2014). Four independent KO lines have been generated for the CB1 recep- tor, encoded by a single large coding exon in the cnr1 gene (exon 2). COMBINATORIAL MOUSE LINES The first three lines were generated with the introduction of a PGK Interbreeding of mutant mouse lines allowed generating combi- or neomycine resistance cassette in the coding region (Ledent et al., natorial mutant mice both within the opioid and the cannabinoid 1999; Zimmer et al., 1999; Robbe et al., 2002). For the fourth line, systems (see references in Table 1). These combinatorial lines loxP sites were introduced flanking exon 2 and this floxed line was constituted useful tools to clarify the specific role of particular further crossed with a line constitutively expressing the Cre recom- components of both systems in reward and analgesia, as well as binase enzyme, therefore generating a full CB1 KO by deletion of to evaluate in vivo selectivity for specific ligands and receptor the sequence between the two lox P sites (Marsicano et al., 2002). subtype identification (Kieffer and Gaveriaux-Ruff, 2002; Nadal These mice were mostly unresponsive to cannabinoid ligands in et al., 2013). Data for reward responses obtained using multi- mediating analgesia, reinforcement, hypothermia, hypolocomo- ple mutants for cannabinoid or opioid components are detailed tion, and hypotension (Valverde and Torrens, 2012; Nadal et al., below. 2013). Two mouse lines were described for the deletion of the cnr2 gene coding for CB2 receptor, one by Zimmer’s team (Jarai et al., COMPENSATORY EFFECTS OF THE NULL MUTATION 1999; Buckley et al., 2000) and the other one by the company Delt- Globally, a normal development was described for the various agen (Wotherspoon et al., 2005). Both were developed by deleting mutant lines, with KO mice being fertile, caring for their off- part of the coding region (in exon 2), leaving the start codon spring, and not showing any major behavioral abnormalities. A with a portion of the amino terminus sequence and aminoacids higher mortality rate was described for one of the CB1 KO line coding for some transmembrane domains of the receptor. In (Zimmer et al., 1999) but not reported for the two others. Inter- these constructions expression of the amino-terminal part of the estingly, among the combinatorial mice, the triple mutant of the CB2 receptor could potentially occur, but in both cases, it was opioid receptors present a striking increase in body weight and shown that the receptor was non-functional in the mutant mice size, but this obese-like phenotype needs further characterization (Dhopeshwarkar and Mackie, 2014). Two mutant lines have been (Befort and Gaveriaux-Ruff, personal communication). Compen- described for the NAPE-PLD enzyme involved in AEA synthesis, satory mechanisms may have developed in some KO animals, but targeting exon 3 (Tsuboi et al., 2011)orexon4(Leung et al., 2006). no systematic studies are available. Deletion of opioid receptors These KO mice have highlighted the complexity of AEA synthe- did not markedly modify the expression or activity of the other sis with both calcium-dependent and -independent mechanisms. opioid receptors or the expression of opioid peptides as described Two isoforms of DAGLα and DAGLβ responsible for the synthesis by the initial characterizations of the distinct mutants lines (see of 2-AG have been described and KO lines have been generated for references in Table 1 and Kitchen et al., 1997; Slowe et al., 1999; each of them with both homologous recombination and gene trap- Oakley et al., 2003). A complete autoradiographic mapping of the ping approaches (Gao et al., 2010; Tanimura et al., 2010; Yoshino delta KO mice indicated decreased binding levels of mu and kappa et al., 2011). The DAGLα KO animals showed a markedly reduced ligands in specific brain areas (Goody et al., 2002). Deletion of opi- 2-AG brain content whereas levels were normal in brain regions oid peptides modified other partners of the opioid system, with a of KO for the β isoform indicating a much greater contribution region-dependent increased of both mu and delta receptor expres- of DAGLα to 2-AG biosynthesis in the central nervous system. sion levels observed in the Penk KO line (Brady et al., 1999; Clarke These mutant mice were particularly useful in the characterization et al., 2003) and for the three opioid receptors in the Pdyn and of DAGL involvement in retrograde endocannabinoid signaling the double Pdyn/Penk mutant line with no additive effects (Clarke

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et al., 2003). Interestingly, specific changes of CB1 receptor expres- together with mice expressing the Cre-recombinase under a spe- sion or activity were reported in mu and delta opioid receptor cific promoter. This allows a time-, organ- or site-specific deletion mutant lines (Berrendero et al., 2003). In the mu KO brain, there of a target gene. This strategy allowed uncoupling the central and was no difference in CB1 expression but a decreased efficacy of peripheral functions of CB1 receptors (Agarwal et al., 2007) and the classical cannabinoid agonist WIN 55,212-2 was observed more recently of mu or delta opioid receptors (Gaveriaux-Ruff specifically in the CPu while both density of CB1 receptor and et al., 2011; Weibel et al., 2013) using the promoter of the channel activation by WIN 55,212-2 increased in substantia nigra of delta Nav1.8 only expressed in DRGs, revealing a key role for these recep- KO animals. tors expressed in primary nociceptive neurons in inflammatory Compensatory effects in KO animals concerning the cannabi- pain. Toinvestigate molecular mechanisms at the level of neuronal noid system have been described both for receptor or catabolic circuitry, selective deletion of a particular gene can also be achieved enzyme KO mice. The invalidation of the CB1 receptor gene was in specific neuronal types. For example, deletion of the delta opi- associated with age-dependent adaptive changes of endocannabi- oid receptors specifically in forebrain GABAergic neurons was noid metabolism, with increased FAAH and AEA membrane obtained by crossing a delta opioid floxed mouse line (Gaveriaux- transporter activities in KO hippocampus and cortex, decreased Ruff et al.,2011) together with a dlx5-6-Cre mouse line, specifically AEA content in hippocampus but no change in 2-AG levels (Di expressing the Cre-recombinase in GABAergic forebrain neurons Marzo et al., 2000; Maccarrone et al., 2001, 2002). In the FAAH in order to investigate the role of these specific delta receptors in KO mice, CB1 receptor mRNA decreased in CPu, nucleus accum- anxiety (Chu Sin Chung et al., 2014). This latter mouse line was bens (core), hippocampus (CA1), hypothalamic nucleus (VMN), previously crossed with the CB1 floxed mice to successfully obtain and amygdala. Its functional activity was also markedly reduced a GABA-CB1 conditional mutant (Monory et al., 2006). These in CPu, the core of nucleus accumbens, and CA3 region of the mutants were also compared with several other cKO bearing a hippocampus (Vinod et al., 2008). Interestingly, reduction of CB1 deletion of CB1 receptor in differing specific neuronal popula- receptor density and activity were also observed in MGL KO mouse tions: forebrain glutamatergic neurons (CB1CamKIIa-Cre mice brain, which may prevent the manifestation of the dramatically or CaMK-CB1KO), cortical glutamatergic neurons (CB1NEX-Cre enhanced 2-AG behavioral effects in these mice (Chanda et al., mice or Glu-CB1KO), both glutamatergic and GABAergic neurons 2010; Schlosburg et al., 2010). In DAGLα- and DAGLβ-KO, no (Glu/GABA-CB1KO) or D1-dopaminergic neurons (CB1Drd1a- difference was reported for CB1 mRNA (Gao et al., 2010)orpro- Cre mice) (Marsicano et al., 2003; Monory et al., 2006, 2007; tein (Tanimura et al., 2010) levels in comparison to WT mice. Bellocchio et al., 2010) for studying the role of CB1 receptors as In these KO mice, CB1 brain functional signaling was unaltered well as behavioral and autonomic effects of the agonist THC. (Aaltonen et al., 2014). To our knowledge, no data is available For the opioid system, a recent study reported the generation for any compensatory effect on CB2 expression or activity in the of a conditional mutant for the kappa opioid receptor, selec- distinct cannabinoid KOs. However, some reports indicate modi- tively deleted in DA-expressing neurons. These kappa cKO mice fications of the opioid system in CB1 KO animals. An increase of showed reduced anxiety-like behavior as well as increased sen- both enkephalin and dynorphin mRNA expression was observed sitivity to cocaine, consistent with a role for kappa receptors in in the striatum (Steiner et al., 1999; Gerald et al., 2006, 2008)as negative regulation of DA function (Van’t Veer et al., 2013). For well as an increase in kappa and delta opioid receptor activities the cannabinoid system, cKO lines were also generated for the without changes in their binding (Uriguen et al., 2005). No com- CB1 receptor to study its specific implication in neurons (Maresz pensatory changes of mRNA levels for the three opioid receptors et al., 2007)orperipheralnerves(Pryce et al., 2014), in serotonin- were reported in dorsal root ganglia or spinal cord of the CB1 ergic (Dubreucq et al., 2012b) or paraventricular (Dubreucq et al., KO animals (Pol et al., 2006). In FAAH KO mice, Penk mRNA 2012a) and ventromedial (Bellocchio et al., 2013) hypothalamic expression was decreased in both CPu and nucleus accumbens neurons. CB1 was also specifically deleted in astroglial cells to which paralleled a reduced mu opioid receptor functional activity investigate its role in working memory and long-term hippocam- (Vinod et al., 2008). Noteworthy, these compensatory alterations pal depression (Han et al., 2012). CB1 was deleted in specific cell of opioid or cannabinoid components in specific regions of the types like hepatocytes to study its role in ethanol-induced fatty mutant lines could account for interactions of the two systems liver (Jeong et al., 2008), lymphocytes (Maresz et al., 2007)orepi- which may be relevant for neuroadaptative processes involved in dermal keratinocytes (Gaffal et al., 2013) to investigate its potential drug dependence. role in regulation of inflammatory responses. Another strategy to generate a cKO mouse is by using viral mediated construct car- CONDITIONAL APPROACHES rying the Cre-recombinase injected directly in the structure of Knockout mice are very useful tools for understanding the interest of a target gene-floxed mouse. For example, the mu opi- contribution of each component of these systems in vari- oid receptor was selectively deleted in the dorsal raphe, the main ous conditions including pain, mood disorders or addiction serotoninergic brain area, and this deletion abolished the develop- (Valverde and Torrens, 2012; Gaveriaux-Ruff, 2013; Lutz and Kief- ment of social withdrawal in a model of heroin abstinence (Lutz fer, 2013b; Nadal et al., 2013; Charbogne et al., 2014). Recent et al., 2014). approaches using gene manipulation in mice have been developed In opposition to the loss of function approach, recent stud- with the widely used Cre-loxP recombinase system to generate ies used a rescue strategy where the target gene is re-expressed cKO (Fowler and Kenny, 2012; Table 2). It consists of crossing in a null mutant, in only a subset of cells (Table 2). This mice whose target genes are floxed (flanked with two loxP sites) helps to provide information concerning the sufficient role of

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Table 2 | Conditional knockout mouse lines for the opioid and the cannabinoid systems.

Target Gene Targeted neurons or structures for selective Targeted neurons or structures for Reference deletion “loss of function” selective expression “rescue”

Opioid system Oprm Primary sensory neurons expressing Nav1.8 channel Weibel et al. (2013) (Nav1.8-Cre) Subpopulation of striatal medium spiny Cui et al. (2014) neurons Oprd Primary sensory neurons expressing Nav1.8 channel Gaveriaux-Ruff et al. (2011) (Nav1.8-Cre) Forebrain GABAergic neurons (Dlx5/6-Cre) Chu Sin Chung et al. (2014) Oprk Dopamine containing neurons (DAT-Cre) Van’t Veer et al. (2013) Cannabinoid system Cnr1 Principal forebrain neurons (CamKII-Cre) Marsicano et al. (2003) Forebrain GABAergic neurons (Dlx5/6-Cre) Monory et al. (2006) Cortical glutamatergic neurons (NEX-Cre) Monory et al. (2006) Glutamatergic and GABAergic neurons (Glu/GABA) Bellocchio et al. (2010) Primary sensory neurons expressing Nav1.8 channel Agarwal et al. (2007) (Nav1.8-Cre) D1-dopaminergic neurons (Drd1a-Cre) Monory et al. (2007) Serotoninergic neurons (TPH2-CreERT2) Dubreucq et al. (2012b) Paraventricular hypothalamic neurons (Sim1-Cre) Dubreucq et al. (2012a) Ventromedial hypothalamic neurons (SF1-cre) Bellocchio et al. (2013) Neurons Nestin (Nes-Cre) Maresz et al. (2007) Peripheral nerve (peripherin-Cre) Pryce et al. (2014) Astrocytes (GFAP- CreERT2) Han et al. (2012) Hepatocytes (Alb-Cre) Jeong et al. (2008) Lymphocytes (lck-Cre) Maresz et al. (2007) Keratinocytes (K14-Cre) Gaffal et al. (2013) Dorsal telencephalic glutamatergic neurons Ruehle et al. (2013) (Glu-CB1-RS) FAAH Nervous system (FAAH-NS) Cravatt et al. (2004)

This table summarizes the recent published reports of cKO mouse lines for the different partners of opioid and cannabinoid systems using “loss of function” or “rescue” strategies. the cell type expressing the target gene for a given function or expressing FAAH under the neural specific enolase promoter establishing whether other cellular subtypes or circuits are nec- (Cravatt et al., 2004). These mice exhibited a discrete subset of essary. When mu opioid receptor were re-expressed only in a the biochemical and behavioral phenotypes observed in FAAH subpopulation of striatal direct-pathway neurons, in a mu KO KO mice providing key insights into the distinct functions played background, it restored opiate reward and opiate-induced stri- by the central and peripheral lipids transmitter signaling systems atal DA release, partially restored motivation to self-administer in vivo. an opiate, but the rescued mice lacked opiate analgesia or with- In conclusion, despite potential limits such as developmental drawal (Cui et al., 2014). In a similar genetic strategy, CB1 receptor effects of the mutation or compensatory mechanisms to over- expression was restored exclusively in dorsal telencephalic glu- come consequences of the mutation, the use of mutants wherein tamatergic neurons and proved sufficient to control neuronal a component of either opioid or cannabinoid system is selectively functions that are in large part hippocampus-dependent, while deleted from restricted neuronal populations provides essential it was insufficient for proper amygdala functions (Ruehle et al., tools for a comprehensive understanding of mechanisms under- 2013). A conditional line where the expression of the FAAH lying cannabinoid or opioid effects in reward circuitry. So far, enzyme has been restricted to the nervous system (FAAH-NS) was these conditional lines for opioid and cannabinoid systems were generated by crossing the FAAH KO line with a transgenic mouse, mostly characterized for pain or emotional behavioral responses,

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and few data is yet to become available for reward aspects THC. A similar protocol was used to induce aversion, but with a (Table 2). higher dose of THC (5 mg/kg ip) wherein mu KO mice showed a decreased CPA (Ghozland et al., 2002). THC-induced CPA was CANNABINOID REINFORCING EFFECTS IN OPIOID abolished in similar conditions in both Pdyn (Zimmer et al., 2001) KNOCKOUT MICE and kappa KO mice (Ghozland et al., 2002). Self-administration For evaluating the effect of cannabinoids in opioid mutant mice, of the synthetic cannabinoid agonist WIN55,212-2 was success- THC-induced CPP was mostly used (Table 3). Interestingly, the fully established in freely moving mice with a low priming dose same protocol was used for all tested opioid KO mice with 1 mg/kg (0.1 mg/kg i.p.,) and with this protocol, Pdyn KO mice showed ip dose with a priming injection in the home cage. In these facilitated SA (Mendizabal et al., 2006). Altogether, these data conditions, no differences in place preference induced by THC was support the idea that the kappa/dynorphin system plays a key observed in delta or kappa KO mice while THC-CPP was abolished role in mediating cannabinoid dysphoric effects and therefore in mu KO mutants (Ghozland et al., 2002)aswellasinthedou- negatively modulates their rewarding effects (Mendizabal et al., ble mu-delta KO mice (Castane et al., 2003). These data support 2006). Contribution of delta receptors in reward appears complex the hypothesis that mu receptors mediate rewarding properties of (Charbogne et al., 2014; Gutierrez-Cuesta et al., 2014) and it has

Table 3 | Rewarding and dependence responses for cannabinoids and opioids measured in KO mouse lines for both systems.

Gene knockout Behavioral response Genotype effect Reference

Opioid system Oprm CPP,THC (1 mg/kg, i.p.) Abolished Ghozland et al. (2002) CPA THC (5 mg/kg, i.p.) Decreased WD, THC (20 mg/kg, i.p. 2x/d, 6d) Unchanged WD, THC (10 mg/kg, s.c. 5d) Unchanged Lichtman et al. (2001) WD, THC (30 or 100 mg/kg, s.c. 5d) Decreased Oprd CPP,THC (1 mg/kg, i.p.) Unchanged Ghozland et al. (2002) CPA THC (5 mg/kg, i.p.) Unchanged WD, THC (20 mg/kg, i.p. 2x/d, 6d) Unchanged Oprm/Oprd CPP,THC (1 mg/kg, i.p.) Decreased Castane et al. (2003) WD, THC (20 mg/kg, i.p. 2x/d, 6d) Decreased Oprk CPP,THC (1 mg/kg, i.p.) Unchanged Ghozland et al. (2002) CPP,THC (1 mg/kg, i.p.)w/o priming Present, absent in WT CPA, THC (5 mg/kg, i.p.) Abolished WD, THC (20 mg/kg, i.p. 2x/d, 6d) Unchanged Penk WD, THC (20 mg/kg, i.p. 2x/d, 6d) Decreased Valverde et al. (2000) Pdyn CPA, THC (5 mg/kg, i.p.) Abolished Ghozland et al. (2002) SA, WIN 55,212(6.25 mg/kg/inf, i.v.) Increased Mendizabal et al. (2006) SA, WIN 55,212(12.5 mg/kg/inf, i.v.) Abolished WD, THC (20 mg/kg, i.p. 2x/d, 6d) Decreased Zimmer et al. (2001) Cannabinoid system Cnr1 CPP,morphine (5 mg/kg, s.c.) Abolished Martin et al. (2000) CPA, morphine + naloxone (20–100 mg/kg i.p. over 6d + 0.1 mg/kg s.c.) Unchanged CPP,morphine (4–8 mg/kg, i.p.) Unchanged Rice et al. (2002) CPA, morphine + naloxone (8 mg/kg + 5 mg/kg, i.p.) Unchanged SA, morphine (2 ug/kg.inf, i.v.) Abolished Cossu et al. (2001) SA, morphine (1, 2, 4 ug/kg/inf, i.v.) Decreased Ledent et al. (1999) WD, morphine (20 mg/kg to 100 mg/kg, 5d) Decreased WD, morphine (75 mg/kg pellet, 5d) Decreased Lichtman et al. (2001) CPA, U50,488H (1 mg/kg, s.c.) Abolished Ledent et al. (1999)

This table summarizes published reports of behavioral responses in reward and precipitated withdrawal for cannabinoids in opioid KO lines and opioids in cannabinoid KO mutants (CPA, conditioned place aversion; CPP,conditioned place preference; d, day; inf, infusion; i.p., intraperitoneal; s.c., subcutaneous; WD, withdrawal; w/o, without).

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not yet been established for cannabinoid reward, neither phar- selective opioid agonists on reward in CB1 KO mice are avail- macologically nor genetically. A potential role of this particular able. Interestingly, it has been demonstrated that the absence of receptor in cannabinoid reward awaits further studies investigating CB1 receptor also results in a reduction of the sensitivity to the either cannabinoid SA (motivation aspects) or delta cKO mutant rewarding properties of sucrose (Sanchis-Segura et al., 2004), as responses (deletion of specific subpopulation of receptors). well as other reinforcers (for recent reviews, see (Lopez-Moreno Another aspect that was explored in opioid KO mice et al., 2010; Maldonado et al., 2013). Together with pharmacologi- is cannabinoid dependence. Upon chronic THC treatment, cal approaches (Maldonado et al.,2006), KO data therefore provide antagonist-induced withdrawal signs measured in WT animals confirmatory support that CB1 receptor play a modulatory role in were unchanged for Pdyn KO (Zimmer et al., 2001) or single the reinforced behaviors maintained by sucrose and some other mutant mice for mu, delta or kappa opioid receptors (Ghoz- reinforcers with, in particular, a mutual interaction of opioid and land et al., 2002). Signs were attenuated in KO animals for Penk cannabinoid systems. (Valverde et al., 2000), for the double mu-delta receptor mutant For the other components of the endocannabinoid system, (Castane et al., 2003)aswellasformureceptorKO,atahighdose no specific data for genetically modified animals were reported (Lichtman et al., 2001)(Table 3). No data are yet available for the for the investigation of opioid reward, although pharmacological other opioid peptide KO mice concerning cannabinoid physical inhibition of the endocannabinoid catabolic enzymes attenuates dependence. Collectively, available data indicate the involvement both naloxone-induced withdrawal as well as spontaneous with- of the enkephalinergic system, with a cooperative action of mu drawal signs in morphine dependent mice (Ramesh et al., 2011, and delta receptors, in the expression of cannabinoid dependence. 2013), indicating a potential role of these enzymes in opioid dependence. OPIOID REINFORCING EFFECTS IN CANNABINOID KNOCKOUT MICE CONCLUSION AND PERSPECTIVES Knockout approaches have greatly improved our knowledge on Globally, despite some compensatory alterations at both opioid the role of CB1 receptors in addiction in general, even though and cannabinoid levels in mutant lines, KO studies have provided contradictory data exist (Maldonado et al., 2006). In particular, insights into the mutual role of both opioid and cannabinoid for opiate responses (Table 3) induced by mu agonists, CB1 KO systems on reward. In particular, these studies have highlighted mice showed no morphine-induced place preference (5 mg/kg, the major role for both mu opioid and CB1 receptors in these s.c., 3 injections over 6 days) (Martin et al., 2000) and a dimin- processes. Clearly, the mu opioid receptor is a convergent molec- ished propensity to self-administer morphine (Ledent et al., 1999; ular target mediating rewarding properties of opioid compounds Cossu et al., 2001). A microdialysis study revealed that morphine- but also of other drugs of abuse, including cannabinoids. CB1 induced increase of extracellular DA was not observed in CB1 receptor also appears as a modulator of opioid reward. On the KO mice (Mascia et al., 1999). Taken together, these data suggest other hand, KO approaches for endogenous opioid peptides or a reduction in morphine’s reinforcing activity in the absence of enzymes for synthesis or degradation of endocannabinoids have the CB1 receptor. Another study could not reveal any changes been very useful to clarify their specific role in both endoge- in place preference using a slightly more intensive conditioning nous systems but less/no data are available for reward mecha- paradigm and a different set up with two doses of morphine (4 nisms. These mutants therefore need further investigations to or 8 mg/kg, four injections over 4 days) (Rice et al., 2002). Inter- clarify their potential implication in cannabinoid/opioid reward estingly, no differences between WT and CB1 KO mice could be aspects. observed in a CPA paradigm where the opioid antagonist naloxone Conventional genetically modified animals have strengthened was used to induce withdrawal in morphine-treated mice via two our current knowledge of the interaction between these two sys- distinct paradigms (Martin et al., 2000; Rice et al., 2002). Upon tems, but further studies using conditional approaches will be chronic morphine treatment, naloxone-induced withdrawal signs necessary to clarify the potential crosstalk existing specifically in measured in WT animals were attenuated (Ledent et al., 1999; reward processes. Interaction between these two neuromodula- Lichtman et al., 2001). Together, these findings suggest that CB1 tor systems may be dependent on the brain area where it occurs, receptors are not involved in the disphoric effects of morphine even inside the brain rewarding networks (Parolaro et al., 2010). withdrawal (CPA) but are noticeably required for the development Both mu opioid and CB1 receptors are highly expressed in these of physical dependence or of somatic signs of opiate withdrawal. networks in similar brain structures and a potential interaction in Surprisingly, other important effects of morphine, like acute areas where they are both strongly expressed is probable. Notice- induced analgesia and tolerance to chronic morphine-induced ably, opposite expression levels are observed in discrete areas analgesia, were not altered in CB1 KO animals. These findings like amygdala (BLA versus central amygdala) as well as habe- together with the data on mu opioid KO mice with cannabinoid nula (medial versus lateral nuclei) and these differences may also treatments suggest a bidirectional influence of mu opioid and CB1 account for a modulatory role of the two systems in reward pro- cannabinoid receptors on reward processes. Aversive effects of the cesses (Figure 1). Approaches using double mutants for both kappa opioid agonist U50,488H were also blunted in CB1 recep- receptors would be useful to further understand their mutual torKOmice(Ledent et al., 1999). Together with the data of kappa role in drug reward. Moreover, in this perspective, conditional opioid and Pdyn KO mice, it indicates that both cannabinoid and approaches will surely provide invaluable insights into opioid and opioid systems modulate negative motivational drug effects. To cannabinoid interaction at the circuitry level. The growing num- our knowledge, no data concerning the specific effect of delta ber of cKO mutant lines becoming available will help this side of

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research. Likewise, the implication of the CB2 receptor in these of rats, an effect associated with changes in mRNA expression interactions has not yet been explored and may be particularly of cannabinoid, DA, and glutamatergic receptor genes in the relevant in specific brain structures. In fact, demonstration of striatum, suggesting adaptations to long-term drug effect and CB2 expression in several brain structures has opened a field of germline transmission, most likely involving epigenetic changes investigation for a possible role in addiction that should help to (Szutorisz et al., 2014). How these neuromodulator systems are reveal potential direct interaction between CB2 and the opioid dependent on various internal and external environmental fac- system. tors, and therefore are involved in epigenetics and whether one G protein coupled receptor can associate as heteromers and system influences the epigenetic machinery to control the other extended research is now directed toward elucidating the phys- system, are unresolved questions for upcoming studies (D’Addario iological role of such heteromers and finding therapeutical et al., 2013). Future investigation in this field will be necessary to approaches targeting these entities (see recent reviews Fujita et al., better delineate the neurobiological mechanisms underlying these 2014; Massotte, 2014). Several lines of evidence have suggested neuroadaptations. interactions between delta or mu opioid receptors and the CB1 receptors. Close vicinity of CB1 receptors with mu or delta ACKNOWLEDGMENTS opioid receptors has recently been established at the neuronal I would like to thank Dr. D. Massotte for constant support and level, suggesting heteromeric formation in vivo and potential fruitful discussions and M. Sturgis for English proof reading of the impact on both receptors signaling properties. A recent study manuscript. I would like to thank funding sources including the demonstrated an important role for the heterodimer CB1-delta Centre National de la Recherche Scientifique and the Université de in neuropathic pain where cortical functions of delta receptor Strasbourg. I would like to dedicate this review to my dear former were altered (Bushlin et al., 2012). CB1 and mu receptors asso- colleague and friend Hans Matthes, who constructed the first mu ciate as heteromers in cultured cells and a recent study showed that opioid knockout mouse, and who passed away unexpectedly this bivalent ligands for both receptors are potent analgesic devoid of summer. tolerance (Le Naour et al., 2013), suggesting potential functional heteromers in pain. Therefore, one can easily predict that similar REFERENCES mechanisms may occur in another pathological state like addic- Aaltonen, N., Riera Ribas, C., Lehtonen, M., Savinainen, J. R., and Laitinen, tion and this opens up new prospects for pharmacological action J. T. (2014). Brain regional cannabinoid CB(1) receptor signalling and alterna- tive enzymatic pathways for 2-arachidonoylglycerol generation in brain sections of cannabinoid and opioid drugs. In this context, it will be critical of diacylglycerol lipase deficient mice. Eur. J. Pharm. Sci. 51, 87–95. doi: to see whether CB2 also plays a role as a potential heteromeric 10.1016/j.ejps.2013.08.035 interactor with opioid receptors. Agarwal, N., Pacher, P., Tegeder, I., Amaya, F., Constantin, C. E., Brenner, G. J., et al. No effective therapeutic approaches for cannabis dependence (2007). Cannabinoids mediate analgesia largely via peripheral type 1 cannabinoid are currently available and opioid addiction therapies are not fully receptorsinnociceptors.Nat. Neurosci. 10, 870–879. doi: 10.1038/nn1916 Ahn, K., Mckinney, M. K., and Cravatt, B. F. (2008). Enzymatic pathways that satisfying for all patients. Further studies are therefore needed regulate endocannabinoid signaling in the nervous system. Chem. Rev. 108, 1687– to clarify the mechanistic basis of interaction of the two sys- 1707. doi: 10.1021/cr0782067 tems, which would aid in the development of drug therapies Ansonoff, M. A., Zhang, J., Czyzyk, T., Rothman, R. B., Stewart, J., Xu, H., et al. to reduce dependence and abuse. Antibodies or bivalent lig- (2006). Antinociceptive and hypothermic effects of salvinorin a are abolished in a ands as mentioned previously represent interesting therapeutic novel strain of kappa-opioid receptor-1 knockout mice. J. Pharmacol. Exp. Ther. 318, 641–648. doi: 10.1124/jpet.106.101998 targets. In addition, dual enkephalinase inhibitors and cannabi- Belin, D., and Deroche-Gamonet, V. (2012). Responses to novelty and vul- noid catabolic enzyme inhibitors have been proposed as attractive nerability to cocaine addiction: contribution of a multi-symptomatic animal therapeutic targets to treat pain (Roques et al., 2012) and such bi- model. Cold Spring Harb. Perspect. Med. 2:a011940. doi: 10.1101/cshperspect.a0 functional compounds may also be relevant as promising strategies 11940. for alleviating dependence. Bellocchio, L., Lafenetre, P., Cannich, A., Cota, D., Puente, N., Grandes, P., et al. (2010). Bimodal control of stimulated food intake by the endocannabinoid Substantial progress has been made in understanding the cel- system. Nat. Neurosci. 13, 281–283. doi: 10.1038/nn.2494 lular and molecular mechanisms of prolonged use of cannabinoid Bellocchio, L., Soria-Gomez, E., Quarta, C., Metna-Laurent, M., Cardinal, P., or opioid drugs (Kreek et al., 2012; Fratta and Fattore, 2013). Binder, E., et al. (2013). Activation of the sympathetic nervous system medi- In addition to their direct role in reward, interaction between ates hypophagic and anxiety-like effects of CB(1) receptor blockade. Proc. Natl. Acad. Sci. U.S.A. 110, 4786–4791. doi: 10.1073/pnas.1218573110 opioid and cannabinoid neuromodulator systems has been pro- Berrendero, F., Mendizabal, V., Murtra, P., Kieffer, B. L., and Maldonado, R. (2003). posed to explain some aspects of vulnerability to addiction and, Cannabinoid receptor and WIN 55 212-2-stimulated [35S]-GTPgammaS binding in this perspective, recent attention has been focused on yet in the brain of mu-, delta-, and kappa-opioid receptor knockout mice. Eur. J. another critical level, epigenetics. These molecular processes, Neurosci. 18, 2197–2202. doi: 10.1046/j.1460-9568.2003.02951.x including methylation of DNA, post-translational modifications Bodnar, R. J. (2014). Endogenous opiates and behavior: 2013. Peptides 62C, 67–136. doi: 10.1016/j.peptides.2014.09.013 of histones and regulation by microRNA, regulate gene expres- Brady, L. S., Herkenham, M., Rothman, R. B., Partilla, J. S., Konig, M., Zimmer, sion and are crucial in long-term adaptations induced by drugs A. M., et al. (1999). Region-specific up-regulation of opioid receptor binding (Nestler, 2014). Recent studies have shown a direct associa- in enkephalin knockout mice. Brain Res. Mol. Brain Res. 68, 193–197. doi: tion between THC-induced Penk upregulation through reduction 10.1016/S0169-328X(99)00090-X Buckley, N. E., Mccoy, K. L., Mezey, E., Bonner, T., Zimmer, A., Felder, C. C., of histone H3 lysine 9 pattern of methylation and increased et al. (2000). Immunomodulation by cannabinoids is absent in mice deficient heroin SA (Tomasiewicz et al., 2012). Adolescent THC-exposure for the cannabinoid CB(2) receptor. Eur. J. Pharmacol. 396, 141–149. doi: also resulted in altered heroin SA in the subsequent generation 10.1016/S0014-2999(00)00211-9

Frontiers in Pharmacology | Neuropharmacology February 2015 | Volume 6 | Article 6 | 10 Befort Opioid and cannabinoid systems interaction in reward

Bushlin, I., Gupta, A., Stockton, S. D. Jr., Miller, L. K., and Devi, L. A. Dinh, T. P., Carpenter, D., Leslie, F. M., Freund, T. F., Katona, I., Sensi, S. L., et al. (2012). Dimerization with cannabinoid receptors allosterically modulates delta (2002). Brain monoglyceride lipase participating in endocannabinoid inactiva- opioid receptor activity during neuropathic pain. PLoS ONE 7:e49789. doi: tion. Proc. Natl. Acad. Sci. U.S.A. 99, 10819–10824. doi: 10.1073/pnas.152334899 10.1371/journal.pone.0049789 Dubreucq, S., Kambire, S., Conforzi, M., Metna-Laurent, M., Cannich, A., Soria- Castane, A., Robledo, P., Matifas, A., Kieffer, B. L., and Maldonado, R. (2003). Gomez, E., et al. (2012a). Cannabinoid type 1 receptors located on single-minded Cannabinoid withdrawal syndrome is reduced in double mu and delta opioid 1-expressing neurons control emotional behaviors. Neuroscience 204, 230–244. receptor knockout mice. Eur. J. Neurosci. 17, 155–159. doi: 10.1046/j.1460- doi: 10.1016/j.neuroscience.2011.08.049 9568.2003.02409.x Dubreucq, S., Matias, I., Cardinal, P., Haring, M., Lutz, B., Marsicano, G., et al. Chanda, P. K., Gao, Y., Mark, L., Btesh, J., Strassle, B. W., Lu, P., et al. (2012b). Genetic dissection of the role of cannabinoid type-1 receptors in the (2010). Monoacylglycerol lipase activity is a critical modulator of the tone and emotional consequences of repeated social stress in mice. Neuropsychopharma- integrity of the endocannabinoid system. Mol. Pharmacol. 78, 996–1003. doi: cology 37, 1885–1900. doi: 10.1038/npp.2012.36 10.1124/mol.110.068304 Erbs, E., Faget, L., Scherrer, G., Matifas, A., Filliol, D., Vonesch, J. L., et al. (2014). A Charbogne, P., Kieffer, B. L., and Befort, K. (2014). 15 years of genetic approaches mu-delta opioid receptor brain atlas reveals neuronal co-occurrence in subcortical in vivo for addiction research: opioid receptor and peptide gene knockout networks. Brain Struct. Funct. doi: 10.1007/s00429-014-0717-9 [Epub ahead of in mouse models of drug abuse. Neuropharmacology 76(Pt B), 204–217. doi: print]. 10.1016/j.neuropharm.2013.08.028 Evans, C. J., Keith, D. E. Jr., Morrison, H., Magendzo, K., and Edwards, R. H. Chu Sin Chung, P., Keyworth, H. L., Martin-Garcia, E., Charbogne, P., Darcq, (1992). Cloning of a delta opioid receptor by functional expression. Science 258, E., Bailey, A., et al. (2014). A novel anxiogenic role for the delta opioid 1952–1955. doi: 10.1126/science.1335167 receptor expressed in GABAergic forebrain neurons. Biol. Psychiatry doi: Everitt, B. J., and Robbins, T. W. (2005). Neural systems of reinforcement for drug 10.1016/j.biopsych.2014.07.033 [Epub ahead of print]. addiction: from actions to habits to compulsion. Nat. Neurosci. 8, 1481–1489. Clarke, S., Czyzyk, T.,Ansonoff, M., Nitsche, J. F., Hsu, M. S., Nilsson, L., et al. (2002). doi: 10.1038/nn1579 Autoradiography of opioid and ORL1 ligands in opioid receptor triple knockout Fattore, L., Cossu, G., Martellotta, C. M., and Fratta, W. (2001). Intravenous self- mice. Eur. J. Neurosci. 16, 1705–1712. doi: 10.1046/j.1460-9568.2002.02239.x administration of the cannabinoid CB1 receptor agonist WIN 55,212-2 in rats. Clarke, S., Zimmer, A., Zimmer, A. M., Hill, R. G., and Kitchen, I. (2003). Region Psychopharmacology (Berl) 156, 410–416. doi: 10.1007/s002130100734 selective up-regulation of micro-, delta- and kappa-opioid receptors but not opi- Fattore, L., Deiana, S., Spano, S. M., Cossu, G., Fadda, P., Scherma, M., et al. (2005). oid receptor-like 1 receptors in the brains of enkephalin and dynorphin knockout Endocannabinoid system and opioid addiction: behavioural aspects. Pharmacol. mice. Neuroscience 122, 479–489. doi: 10.1016/j.neuroscience.2003.07.011 Biochem. Behav. 81, 343–359. doi: 10.1016/j.pbb.2005.01.031 Contet, C., Kieffer, B. L., and Befort, K. (2004). Mu opioid receptor: a gateway to drug Fattore, L., and Fratta, W. (2011). Beyond THC: the new generation of cannabinoid addiction. Curr. Opin. Neurobiol. 14, 370–378. doi: 10.1016/j.conb.2004.05.005 designer drugs. Front. Behav. Neurosci. 5:60. doi: 10.3389/fnbeh.2011.00060 Cossu, G., Ledent, C., Fattore, L., Imperato, A., Bohme, G. A., Parmentier, M., Fernandez-Ruiz, J., Hernandez, M., and Ramos, J. A. (2010). Cannabinoid- et al. (2001). Cannabinoid CB1 receptor knockout mice fail to self-administer dopamine interaction in the pathophysiology and treatment of CNS disorders. morphine but not other drugs of abuse. Behav. Brain Res. 118, 61–65. doi: CNS Neurosci. Ther. 16, e72–e91. doi: 10.1111/j.1755-5949.2010.00144.x 10.1016/S0166-4328(00)00311-9 Ferre, S., Lluis, C., Justinova, Z., Quiroz, C., Orru, M., Navarro, G., et al. (2010). Cravatt, B. F., Demarest, K., Patricelli, M. P., Bracey, M. H., Giang, D. K., Martin, Adenosine-cannabinoid receptor interactions. Implications for striatal function. B. R., et al. (2001). Supersensitivity to anandamide and enhanced endogenous Br. J. Pharmacol. 160, 443–453. doi: 10.1111/j.1476-5381.2010.00723.x cannabinoid signaling in mice lacking fatty acid amide hydrolase. Proc. Natl. Filizola, M., and Devi, L. A. (2014). Grand opening of structure-guided design for Acad. Sci. U.S.A. 98, 9371–9376. doi: 10.1073/pnas.161191698 novel opioids. Trends Pharmacol. Sci. 34, 6–12. doi: 10.1016/j.tips.2012.10.002 Cravatt, B. F., Giang, D. K., Mayfield, S. P., Boger, D. L., Lerner, R. A., and Gilula, N. B. Filliol, D., Ghozland, S., Chluba, J., Martin, M., Matthes, H. W., Simonin, F., (1996). Molecular characterization of an enzyme that degrades neuromodulatory et al. (2000). Mice deficient for delta- and mu-opioid receptors exhibit opposing fatty-acid amides. Nature 384, 83–87. doi: 10.1038/384083a0 alterations of emotional responses. Nat. Genet. 25, 195–200. doi: 10.1038/76061 Cravatt, B. F., Saghatelian, A., Hawkins, E. G., Clement, A. B., Bracey, M. H., and Flores, A., Maldonado, R., and Berrendero, F. (2014). The hypocretin/orexin Lichtman, A. H. (2004). Functional disassociation of the central and peripheral receptor-1 as a novel target to modulate cannabinoid reward. Biol. Psychiatry fatty acid amide signaling systems. Proc. Natl. Acad. Sci. U.S.A. 101, 10821–10826. 75, 499–507. doi: 10.1016/j.biopsych.2013.06.012 doi: 10.1073/pnas.0401292101 Fowler, C. D., and Kenny, P. J. (2012). Utility of genetically modified mice for Cui, Y., Ostlund, S. B., James, A. S., Park, C. S., Ge, W., Roberts, K. W., et al. (2014). understanding the neurobiology of substance use disorders. Hum. Genet. 131, Targeted expression of mu-opioid receptors in a subset of striatal direct-pathway 941–957. doi: 10.1007/s00439-011-1129-z neurons restores opiate reward. Nat. Neurosci. 17, 254–261. doi: 10.1038/n Fratta, W., and Fattore, L. (2013). Molecular mechanisms of cannabinoid addiction. n.3622 Curr. Opin. Neurobiol. 23, 487–492. doi: 10.1016/j.conb.2013.02.002 D’Addario, C., Di Francesco, A., Pucci, M., Finazzi Agro, A., and Maccarrone, M. Frazier, C. J. (2011). Key questions of endocannabinoid signalling in the CNS: which, (2013). Epigenetic mechanisms and endocannabinoid signalling. FEBS J. 280, where and when? J. Physiol. 589, 4807–4808. doi: 10.1113/jphysiol.2011.219493 1905–1917. doi: 10.1111/febs.12125 Fujita, W., Gomes, I., and Devi, L. A. (2014). Revolution in GPCR signalling: De Luca, M. A., Valentini, V., Bimpisidis, Z., Cacciapaglia, F., Caboni, P., and Di opioid receptor heteromers as novel therapeutic targets: IUPHAR review 10. Br. Chiara, G. (2014). Endocannabinoid 2-arachidonoylglycerol self-administration J. Pharmacol. 171, 4155–4176. doi: 10.1111/bph.12798 by sprague-dawley rats and stimulation of in vivo dopamine transmission in the Gaffal, E., Cron, M., Glodde, N., Bald, T., Kuner, R., Zimmer, A., et al. (2013). nucleus accumbens Shell. Front. Psychiatry 5:140. doi: 10.3389/fpsyt.2014.00140 Cannabinoid 1 receptors in keratinocytes modulate proinflammatory chemokine De Petrocellis, L., and Di Marzo, V. (2010). Non-CB1, non-CB2 receptors secretion and attenuate contact allergic inflammation. J. Immunol. 190, 4929– for endocannabinoids, plant cannabinoids, and synthetic cannabimimetics: 4936. doi: 10.4049/jimmunol.1201777 focus on G-protein-coupled receptors and transient receptor potential channels. Gao, Y., Vasilyev, D. V., Goncalves, M. B., Howell, F. V., Hobbs, C., Reisenberg, M., J. Neuroimmune Pharmacol. 5, 103–121. doi: 10.1007/s11481-009-9177-z et al. (2010). Loss of retrograde endocannabinoid signaling and reduced adult Dhopeshwarkar, A., and Mackie, K. (2014). CB2 cannabinoid receptors as a ther- neurogenesis in diacylglycerol lipase knock-out mice. J. Neurosci. 30, 2017–2024. apeutic target-what does the future hold? Mol. Pharmacol. 86, 430–437. doi: doi: 10.1523/JNEUROSCI.5693-09.2010 10.1124/mol.114.094649 Gardner, E. L. (2005). Endocannabinoid signaling system and brain reward: Di Marzo, V., Breivogel, C. S., Tao, Q., Bridgen, D. T., Razdan, R. K., Zimmer, A. M., emphasis on dopamine. Pharmacol. Biochem. Behav. 81, 263–284. doi: et al. (2000). Levels, metabolism, and pharmacological activity of anandamide 10.1016/j.pbb.2005.01.032 in CB(1) cannabinoid receptor knockout mice: evidence for non-CB(1), non- Gaveriaux-Ruff, C. (2013). Opiate-induced analgesia: contributions from mu, delta CB(2) receptor-mediated actions of anandamide in mouse brain. J. Neurochem. and kappa opioid receptors mouse mutants. Curr. Pharm. Des 19, 7373–7381. 75, 2434–2444. doi: 10.1046/j.1471-4159.2000.0752434.x doi: 10.2174/138161281942140105163727

www.frontiersin.org February 2015 | Volume 6 | Article 6 | 11 Befort Opioid and cannabinoid systems interaction in reward

Gaveriaux-Ruff, C., Nozaki, C., Nadal, X., Hever, X. C., Weibel, R., Matifas, A., et al. Koob, G. F., and Volkow, N. D. (2010). Neurocircuitry of addiction. Neuropsy- (2011). Genetic ablation of delta opioid receptors in nociceptive sensory neurons chopharmacology 35, 217–238. doi: 10.1038/npp.2009.110 increases chronic pain and abolishes opioid analgesia. Pain 152, 1238–1248. doi: Kreek, M. J., Levran, O., Reed, B., Schlussman, S. D., Zhou, Y., and Butelman, 10.1016/j.pain.2010.12.031 E. R. (2012). Opiate addiction and cocaine addiction: underlying molecular Gerald, T. M., Howlett, A. C., Ward, G. R., Ho, C., and Franklin, S. O. (2008). neurobiology and genetics. J. Clin. Invest. 122, 3387–3393. doi: 10.1172/JCI60390 Gene expression of opioid and dopamine systems in mouse striatum: effects Le Merrer, J., Becker, J. A., Befort, K., and Kieffer, B. L. (2009). Reward pro- of CB1 receptors, age and sex. Psychopharmacology (Berl.) 198, 497–508. doi: cessing by the opioid system in the brain. Physiol. Rev. 89, 1379–1412. doi: 10.1007/s00213-008-1141–1148 10.1152/physrev.00005.2009 Gerald, T. M., Ward, G. R., Howlett, A. C., and Franklin, S. O. (2006). Le Naour, M., Akgun, E., Yekkirala, A., Lunzer, M. M., Powers, M. D., Kalyuzhny, CB1 knockout mice display significant changes in striatal opioid peptide A. E., et al. (2013). Bivalent ligands that target mu opioid (MOP) and cannabi- and D4 dopamine receptor gene expression. Brain Res. 1093, 20–24. doi: noid1 (CB1) receptors are potent analgesics devoid of tolerance. J. Med. Chem. 10.1016/j.brainres.2006.03.088 56, 5505–5513. doi: 10.1021/jm4005219 Ghozland, S., Matthes, H. W., Simonin, F., Filliol, D., Kieffer, B. L., and Maldonado, Ledent, C., Valverde, O., Cossu, G., Petitet, F., Aubert, J. F., Beslot, F., et al. (1999). R. (2002). Motivational effects of cannabinoids are mediated by mu-opioid and Unresponsiveness to cannabinoids and reduced addictive effects of opiates in kappa-opioid receptors. J. Neurosci. 22, 1146–1154. CB1 receptor knockout mice. Science 283, 401–404. doi: 10.1126/science.283.54 Gong, J. P., Onaivi, E. S., Ishiguro, H., Liu, Q. R., Tagliaferro, P. A., Brusco, A., 00.401 et al. (2006). Cannabinoid CB2 receptors: immunohistochemical localization in Leshner, A. I. (1997). Addiction is a brain disease, and it matters. Science 278, 45–47. rat brain. Brain Res. 1071, 10–23. doi: 10.1016/j.brainres.2005.11.035 doi: 10.1126/science.278.5335.45 Goody, R. J., Oakley, S. M., Filliol, D., Kieffer, B. L., and Kitchen, I. Leung, D., Saghatelian, A., Simon, G. M., and Cravatt, B. F. (2006). Inactivation (2002). Quantitative autoradiographic mapping of opioid receptors in the of N-acyl phosphatidylethanolamine phospholipase D reveals multiple mecha- brain of delta-opioid receptor gene knockout mice. Brain Res. 945, 9–19. doi: nisms for the biosynthesis of endocannabinoids. Biochemistry 45, 4720–4726. 10.1016/S0006-8993(02)02452-6 doi: 10.1021/bi060163l Gustavsson, A., Svensson, M., Jacobi, F., Allgulander, C., Alonso, J., Beghi, E., et al. Lichtman, A. H., Sheikh, S. M., Loh, H. H., and Martin, B. R. (2001). (2011). Cost of disorders of the brain in Europe 2010. Eur. Neuropsychopharmacol. Opioid and cannabinoid modulation of precipitated withdrawal in delta(9)- 21, 718–779. doi: 10.1016/j.euroneuro.2011.08.008 tetrahydrocannabinol and morphine-dependent mice. J. Pharmacol. Exp. Ther. Gutierrez-Cuesta, J., Burokas, A., Mancino, S., Kummer, S., Martin-Garcia, E., 298, 1007–1014. and Maldonado, R. (2014). Effects of genetic deletion of endogenous opioid Liu, J., Wang, L., Harvey-White, J., Huang, B. X., Kim, H. Y., Luquet, S., system components on the reinstatement of cocaine-seeking behavior in mice. et al. (2008). Multiple pathways involved in the biosynthesis of anandamide. Neuropsychopharmacology. doi: 10.1038/npp.2014.149 Neuropharmacology 54, 1–7. doi: 10.1016/j.neuropharm.2007.05.020 Han, J., Kesner, P., Metna-Laurent, M., Duan, T., Xu, L., Georges, F., Loacker, S., Sayyah, M., Wittmann, W., Herzog, H., and Schwarzer, C. (2007). et al. (2012). Acute cannabinoids impair working memory through astroglial Endogenous dynorphin in epileptogenesis and epilepsy: anticonvulsant net CB1 receptor modulation of hippocampal LTD. Cell 148, 1039–1050. doi: effect via kappa opioid receptors. Brain 130, 1017–1028. doi: 10.1093/brain/ 10.1016/j.cell.2012.01.037 awl384 Hough, L. B., Nalwalk, J. W., Chen, Y., Schuller, A., Zhu, Y., Zhang, J., Loh, H. H., Liu, H. C., Cavalli, A., Yang, W., Chen, Y. F., and Wei, L. N. (1998). et al. (2000). Improgan, a cimetidine analog, induces morphine-like antinoci- mu Opioid receptor knockout in mice: effects on ligand-induced analgesia and ception in opioid receptor-knockout mice. Brain Res. 880, 102–108. doi: morphine lethality. Brain Res. Mol. Brain Res. 54, 321–326. doi: 10.1016/S0169- 10.1016/S0006-8993(00)02776-1 328X(97)00353-7 Ignatowska-Jankowska, B. M., Muldoon, P. P., Lichtman, A. H., and Damaj, M. I. Lopez-Moreno, J. A., Lopez-Jimenez, A., Gorriti, M. A., and De Fonseca, F.R. (2010). (2013). The cannabinoid CB2 receptor is necessary for nicotine-conditioned place Functional interactions between endogenous cannabinoid and opioid systems: preference, but not other behavioral effects of nicotine in mice. Psychopharma- focus on alcohol, genetics and drug-addicted behaviors. Curr. Drug Targets 11, cology (Berl) 229, 591–601. doi: 10.1007/s00213-013-3117-6 406–428. doi: 10.2174/138945010790980312 Jarai, Z., Wagner, J. A., Varga, K., Lake, K. D., Compton, D. R., Martin, B. R., et al. Lutz, P. E., Ayranci, G., Chu-Sin-Chung, P., Matifas, A., Koebel, P., Filliol, (1999). Cannabinoid-induced mesenteric vasodilation through an endothelial D., et al. (2014). Distinct mu, delta, and kappa opioid receptor mechanisms site distinct from CB1 or CB2 receptors. Proc. Natl. Acad. Sci. U.S.A. 96, 14136– underlie low sociability and depressive-like behaviors during heroin abstinence. 14141. doi: 10.1073/pnas.96.24.14136 Neuropsychopharmacology 39, 2694–2705. doi: 10.1038/npp.2014.126 Jeong, W. I., Osei-Hyiaman, D., Park, O., Liu, J., Batkai, S., Mukhopadhyay, P., Lutz, P. E., and Kieffer, B. L. (2013a). The multiple facets of opioid receptor et al. (2008). Paracrine activation of hepatic CB1 receptors by stellate cell-derived function: implications for addiction. Curr. Opin. Neurobiol. 23, 473–479. doi: endocannabinoids mediates alcoholic fatty liver. Cell Metab. 7, 227–235. doi: 10.1016/j.conb.2013.02.005 10.1016/j.cmet.2007.12.007 Lutz, P. E., and Kieffer, B. L. (2013b). Opioid receptors: distinct roles in Kieffer, B. L. (1995). Recent advances in molecular recognition and signal trans- mood disorders. Trends Neurosci. 36, 195–206. doi: 10.1016/j.tins.2012. duction of active peptides: receptors for opioid peptides. Cell Mol. Neurobiol. 15, 11.002 615–635. doi: 10.1007/BF02071128 Maccarrone, M., Attina, M., Bari, M., Cartoni, A., Ledent, C., and Finazzi-Agro, Kieffer, B. L., Befort, K., Gaveriaux-Ruff, C., and Hirth, C. G. (1992). The A. (2001). Anandamide degradation and N-acylethanolamines level in wild-type delta-opioid receptor: isolation of a cDNA by expression cloning and pharma- and CB1 cannabinoid receptor knockout mice of different ages. J. Neurochem. 78, cological characterization. Proc. Natl. Acad. Sci. U.S.A. 89, 12048–12052. doi: 339–348. doi: 10.1046/j.1471-4159.2001.00413.x 10.1073/pnas.89.24.12048 Maccarrone, M., Valverde, O., Barbaccia, M. L., Castane, A., Maldonado, R., Ledent, Kieffer, B. L., and Gaveriaux-Ruff, C. (2002). Exploring the opioid system by gene C., et al. (2002). Age-related changes of anandamide metabolism in CB1 cannabi- knockout. Prog. Neurobiol. 66, 285–306. doi: 10.1016/S0301-0082(02)00008-4 noid receptor knockout mice: correlation with behaviour. Eur. J. Neurosci. 15, Kitchen, I., Slowe, S. J., Matthes, H. W., and Kieffer, B. (1997). Quantitative 1178–1186. doi: 10.1046/j.1460-9568.2002.01957.x autoradiographic mapping of mu-, delta-, and kappa-opioid receptors in knock- Mackie, K. (2005). Distribution of cannabinoid receptors in the central and out mice lacking the mu-opioid receptor gene. Brain Res. 778, 73–88. doi: peripheral nervous system. Handb. Exp. Pharmacol. 299–325. 10.1016/S0006-8993(97)00988-8 Mackie, K. (2008). Cannabinoid receptors: where they are and what they do. Konig, M., Zimmer, A. M., Steiner, H., Holmes, P. V., Crawley, J. N., Brownstein, J. Neuroendocrinol. 20(Suppl. 1), 10–14. doi: 10.1111/j.1365-2826.2008.01671.x M. J., et al. (1996). Pain responses, anxiety and aggression in mice deficient in Maldonado, R. (2002). Study of cannabinoid dependence in animals. Pharmacol. pre-proenkephalin. Nature 383, 535–538. doi: 10.1038/383535a0 Ther. 95, 153–164. doi: 10.1016/S0163-7258(02)00254-1 Koob, G. F. (2009). Neurobiological substrates for the dark side of com- Maldonado, R., Berrendero, F., Ozaita, A., and Robledo, P. (2011). Neu- pulsivity in addiction. Neuropharmacology 56(Suppl. 1), 18–31. doi: rochemical basis of cannabis addiction. Neuroscience 181, 1–17. doi: 10.1016/j.neuropharm.2008.07.043 10.1016/j.neuroscience.2011.02.035

Frontiers in Pharmacology | Neuropharmacology February 2015 | Volume 6 | Article 6 | 12 Befort Opioid and cannabinoid systems interaction in reward

Maldonado, R., Blendy, J. A., Tzavara, E., Gass, P., Roques, B. P., Hanoune, J., Nadal, X., La Porta, C., Andreea Bura, S., and Maldonado, R. (2013). Involve- et al. (1996). Reduction of morphine abstinence in mice with a mutation in ment of the opioid and cannabinoid systems in pain control: new insights from the gene encoding CREB. Science 273, 657–659. doi: 10.1126/science.273.527 knockout studies. Eur. J. Pharmacol. 716, 142–157. doi: 10.1016/j.ejphar.2013. 5.657 01.077 Maldonado, R., Robledo, P., and Berrendero, F. (2013). Endocannabinoid system Navarrete, F., Rodriguez-Arias, M., Martin-Garcia, E., Navarro, D., Garcia- and drug addiction: new insights from mutant mice approaches. Curr. Opin. Gutierrez, M. S., Aguilar, M. A., et al. (2013). Role of CB2 cannabinoid Neurobiol. 23, 480–486. doi: 10.1016/j.conb.2013.02.004 receptors in the rewarding, reinforcing, and physical effects of nicotine. Maldonado, R., Valverde, O., and Berrendero, F. (2006). Involvement of the Neuropsychopharmacology 38, 2515–2524. doi: 10.1038/npp.2013.157 endocannabinoid system in drug addiction. Trends Neurosci. 29, 225–232. doi: Nestler, E. J. (2014). Epigenetic mechanisms of drug addiction. Neuropharmacology 10.1016/j.tins.2006.01.008 76 Pt B, 259–268. doi: 10.1016/j.neuropharm.2013.04.004 Mansour, A., Fox, C. A., Akil, H., and Watson, S. J. (1995). Opioid-receptor Niikura, K., Narita, M., Okutsu, D., Tsurukawa, Y., Nanjo, K., Kurahashi, K., mRNA expression in the rat CNS: anatomical and functional implications. Trends et al. (2008). Implication of endogenous beta-endorphin in the inhibition of Neurosci. 18, 22–29. doi: 10.1016/0166-2236(95)93946-U the morphine-induced rewarding effect by the direct activation of spinal protein Manzanares, J., Corchero, J., Romero, J., Fernandez-Ruiz, J. J., Ramos, J. A., kinase C in mice. Neurosci. Lett. 433, 54–58. doi: 10.1016/j.neulet.2007.12.042 and Fuentes, J. A. (1999). Pharmacological and biochemical interactions Nogueiras, R., Romero-Pico, A., Vazquez, M. J., Novelle, M. G., Lopez, M., and between opioids and cannabinoids. Trends Pharmacol. Sci. 20, 287–294. doi: Dieguez, C. (2014). The opioid system and food intake: homeostatic and hedonic 10.1016/S0165-6147(99)01339-5 mechanisms. Obes. Facts 5, 196–207. doi: 10.1159/000338163 Maresz, K., Pryce, G., Ponomarev, E. D., Marsicano, G., Croxford, J. L., Shriver, Oakley, S. M., Toth, G., Borsodi, A., Kieffer, B. L., and Kitchen, I. (2003). G-protein L. P., et al. (2007). Direct suppression of CNS autoimmune inflammation via the coupling of delta-opioid receptors in brains of mu-opioid receptor knockout cannabinoid receptor CB1 on neurons and CB2 on autoreactive T cells. Nat. Med. mice. Eur. J. Pharmacol. 466, 91–98. doi: 10.1016/S0014-2999(03)01531-0 13, 492–497. doi: 10.1038/nm1561 Ohno-Shosaku, T., and Kano, M. (2014). Endocannabinoid-mediated retrograde Marsicano, G., Goodenough, S., Monory, K., Hermann, H., Eder, M., Cannich, modulation of synaptic transmission. Curr. Opin. Neurobiol. 29C, 1–8. doi: A., et al. (2003). CB1 cannabinoid receptors and on-demand defense against 10.1016/j.conb.2014.03.017 excitotoxicity. Science 302, 84–88. doi: 10.1126/science.1088208 Onaivi, E. S., Ishiguro, H., Gong, J. P., Patel, S., Perchuk, A., Meozzi, P. A., Marsicano, G., Wotjak, C. T., Azad, S. C., Bisogno, T., Rammes, G., Cascio, M. G., et al. (2006). Discovery of the presence and functional expression of cannabi- et al. (2002). The endogenous cannabinoid system controls extinction of aversive noid CB2 receptors in brain. Ann. N. Y. Acad. Sci. 1074, 514–536. doi: memories. Nature 418, 530–534. doi: 10.1038/nature00839 10.1196/annals.1369.052 Martellotta, M. C., Cossu, G., Fattore, L., Gessa, G. L., and Fratta, W. (1998). Self- Ortega-Alvaro, A., Ternianov, A., Aracil-Fernandez, A., Navarrete, F., Garcia- administration of the cannabinoid receptor agonist WIN 55,212-2 in drug-naive Gutierrez, M. S., and Manzanares, J. (2013). Role of cannabinoid CB receptor mice. Neuroscience 85, 327–330. doi: 10.1016/S0306-4522(98)00052-9 in the reinforcing actions of ethanol. Addict. Biol. doi: 10.1111/adb.12076 Martin, M., Ledent, C., Parmentier, M., Maldonado, R., and Valverde, O. (2000). Pan, Y. X., Xu, J., Xu, M., Rossi, G. C., Matulonis, J. E., and Pasternak, G. W. (2009). Cocaine, but not morphine, induces conditioned place preference and sensi- Involvement of exon 11-associated variants of the mu opioid receptor MOR-1 in tization to locomotor responses in CB1 knockout mice. Eur. J. Neurosci. 12, heroin, but not morphine, actions. Proc. Natl. Acad. Sci. U.S.A. 106, 4917–4922. 4038–4046. doi: 10.1046/j.1460-9568.2000.00287.x doi: 10.1073/pnas.0811586106 Mascia, M. S., Obinu, M. C., Ledent, C., Parmentier, M., Bohme, G. A., Imperato, Panagis, G., Mackey, B., and Vlachou, S. (2014). Cannabinoid regulation of brain A., et al. (1999). Lack of morphine-induced dopamine release in the nucleus reward processing with an emphasis on the role of CB1 receptors: a step back into accumbens of cannabinoid CB(1) receptor knockout mice. Eur. J. Pharmacol 383, the future. Front. Psychiatry 5:92. doi: 10.3389/fpsyt.2014.00092 R1–R2. doi: 10.1016/S0014-2999(99)00656-1 Panlilio, L. V., and Goldberg, S. R. (2007). Self-administration of drugs in animals Massotte, D. (2014). In vivo opioid receptor heteromerization: where do we stand? and humans as a model and an investigative tool. Addiction 102, 1863–1870. doi: Br. J. Pharmacol. 172, 420–434. doi: 10.1111/bph.12702 10.1111/j.1360-0443.2007.02011.x Matsuda, L. A., Lolait, S. J., Brownstein, M. J., Young, A. C., and Bonner, T. I. Panlilio, L. V., Justinova, Z., and Goldberg, S. R. (2010). Animal models of (1990). Structure of a cannabinoid receptor and functional expression of the cannabinoid reward. Br. J. Pharmacol. 160, 499–510. doi: 10.1111/j.1476- cloned cDNA. Nature 346, 561–564. doi: 10.1038/346561a0 5381.2010.00775.x Matthes, H. W., Maldonado, R., Simonin, F., Valverde, O., Slowe, S., Kitchen, I., Parolaro, D., Rubino, T., Vigano, D., Massi, P., Guidali, C., and Realini, N. (2010). et al. (1996). Loss of morphine-induced analgesia, reward effect and withdrawal Cellular mechanisms underlying the interaction between cannabinoid and opioid symptoms in mice lacking the mu-opioid-receptor gene. Nature 383, 819–823. system. Curr. Drug Targets 11, 393–405. doi: 10.2174/138945010790980367 doi: 10.1038/383819a0 Pattij, T., and De Vries, T. J. (2013). The role of impulsivity in relapse vulnerability. Mendizabal, V., Zimmer, A., and Maldonado, R. (2006). Involvement of Curr. Opin. Neurobiol. 23, 700–705. doi: 10.1016/j.conb.2013.01.023 kappa/dynorphin system in WIN 55,212-2 self-administration in mice. Neuropsy- Pertwee, R. G. (2010). Receptors and channels targeted by synthetic cannabi- chopharmacology 31, 1957–1966. doi: 10.1038/sj.npp.1300957 noid receptor agonists and antagonists. Curr. Med. Chem 17, 1360–1381. doi: Mestek, A., Hurley, J. H., Bye, L. S., Campbell, A. D., Chen, Y., Tian, M., et al. (1995). 10.2174/092986710790980050 The human mu opioid receptor: modulation of functional desensitization by Petrenko, A. B., Yamazaki, M., Sakimura, K., Kano, M., and Baba, H. calcium/calmodulin-dependent protein kinase and protein kinase C. J. Neurosci. (2014). Augmented tonic pain-related behavior in knockout mice lack- 15, 2396–2406. ing monoacylglycerol lipase, a major degrading enzyme for the endo- Mizoguchi, H., Watanabe, C., Osada, S., Yoshioka, M., Aoki, Y., Natsui, S., et al. cannabinoid 2-arachidonoylglycerol. Behav. Brain Res. 271, 51–58. doi: (2010). Lack of a rewarding effect and a locomotor-enhancing effect of the selec- 10.1016/j.bbr.2014.05.063 tive mu-opioid receptor agonist amidino-TAPA. Psychopharmacology (Berl) 212, Piomelli, D. (2014). More surprises lying ahead. The endocannabi- 215–225. doi: 10.1007/s00213-010-1946-0 noids keep us guessing. Neuropharmacology 76 Pt B, 228–234. doi: Monory, K., Blaudzun, H., Massa, F., Kaiser, N., Lemberger, T., Schutz, G., 10.1016/j.neuropharm.2013.07.026 et al. (2007). Genetic dissection of behavioural and autonomic effects of Pol, O., Murtra, P., Caracuel, L., Valverde, O., Puig, M. M., and Maldonado, Delta(9)-tetrahydrocannabinol in mice. PLoS Biol. 5:e269. doi: 10.1371/jour- R. (2006). Expression of opioid receptors and c-fos in CB1 knockout mice nal.pbio.0050269 exposed to neuropathic pain. Neuropharmacology 50, 123–132. doi: 10.1016/j. Monory, K., Massa, F., Egertova, M., Eder, M., Blaudzun, H., Westenbroek, R., et al. neuropharm.2005.11.002 (2006). The endocannabinoid system controls key epileptogenic circuits in the Pradhan, A. A., Befort, K., Nozaki, C., Gaveriaux-Ruff, C., and Kieffer, B. L. (2011). hippocampus. Neuron 51, 455–466. doi: 10.1016/j.neuron.2006.07.006 The delta opioid receptor: an evolving target for the treatment of brain disorders. Munro, S., Thomas, K. L., and Abu-Shaar, M. (1993). Molecular characterization Trends Pharmacol. Sci. 32, 581–590. doi: 10.1016/j.tips.2011.06.008 of a peripheral receptor for cannabinoids. Nature 365, 61–65. doi: 10.1038/ Pryce, G., Visintin, C., Ramagopalan, S. V., Al-Izki, S., De Faveri, L. E., Nuamah, 365061a0 R. A., et al. (2014). Control of spasticity in a multiple sclerosis model using

www.frontiersin.org February 2015 | Volume 6 | Article 6 | 13 Befort Opioid and cannabinoid systems interaction in reward

central nervous system-excluded CB1 cannabinoid receptor agonists. FASEB J. Simonin, F., Slowe, S., Becker, J. A., Matthes, H. W., Filliol, D., Chluba, J., et al. 28, 117–130. doi: 10.1096/fj.13–239442 (2001). Analysis of [3H]bremazocine binding in single and combinatorial opioid Ragnauth, A., Schuller, A., Morgan, M., Chan, J., Ogawa, S., Pintar, J., et al. (2001). receptor knockout mice. Eur. J. Pharmacol. 414, 189–195. doi: 10.1016/S0014- Female preproenkephalin-knockout mice display altered emotional responses. 2999(01)00822-6 Proc. Natl. Acad. Sci. U.S.A. 98, 1958–1963. doi: 10.1073/pnas.041598498 Simonin, F., Valverde, O., Smadja, C., Slowe, S., Kitchen, I., Dierich, A., et al. (1998). Ramesh, D., Gamage, T. F., Vanuytsel, T., Owens, R. A., Abdullah, R. A., Disruption of the kappa-opioid receptor gene in mice enhances sensitivity to Niphakis, M. J., et al. (2013). Dual inhibition of endocannabinoid catabolic chemical visceral pain, impairs pharmacological actions of the selective kappa- enzymes produces enhanced antiwithdrawal effects in morphine-dependent agonist U-50,488H and attenuates morphine withdrawal. EMBO J. 17, 886–897. mice. Neuropsychopharmacology 38, 1039–1049. doi: 10.1038/npp.2012.269 doi: 10.1093/emboj/17.4.886 Ramesh, D., Ross, G. R., Schlosburg, J. E., Owens, R. A., Abdullah, R. A., Kinsey, Skoubis, P. D., Lam, H. A., Shoblock, J., Narayanan, S., and Maidment, N. T. S. G., et al. (2011). Blockade of endocannabinoid hydrolytic enzymes attenuates (2005). Endogenous enkephalins, not endorphins, modulate basal hedonic state precipitated opioid withdrawal symptoms in mice. J. Pharmacol. Exp. Ther. 339, in mice. Eur. J. Neurosci. 21, 1379–1384. doi: 10.1111/j.1460-9568.2005.03 173–185. doi: 10.1124/jpet.111.181370 956.x Rice, O. V., Gordon, N., and Gifford, A. N. (2002). Conditioned place preference to Slowe, S. J., Simonin, F., Kieffer, B., and Kitchen, I. (1999). Quantitative morphine in cannabinoid CB1 receptor knockout mice. Brain Res. 945, 135–138. autoradiography of mu-delta- and kappa1 opioid receptors in kappa-opioid doi: 10.1016/S0006-8993(02)02890-1 receptor knockout mice. Brain Res. 818, 335–345. doi: 10.1016/S0006-8993(98)0 Robbe, D., Kopf, M., Remaury, A., Bockaert, J., and Manzoni, O. J. (2002). Endoge- 1201-3 nous cannabinoids mediate long-term synaptic depression in the nucleus accum- Solinas, M., Goldberg, S. R., and Piomelli, D. (2008). The endocannabi- bens. Proc. Natl. Acad. Sci. U.S.A. 99, 8384–8388. doi: 10.1073/pnas.122149199 noid system in brain reward processes. Br. J. Pharmacol. 154, 369–383. doi: Robinson, T. E., and Berridge, K. C. (2008). Review. The incentive sensitization 10.1038/bjp.2008.130 theory of addiction: some current issues. Philos. Trans. R. Soc. Lond. B Biol. Sci. Sora, I., Elmer, G., Funada, M., Pieper, J., Li, X. F., Hall, F. S., et al. (2001). Mu 363, 3137–3146. doi: 10.1098/rstb.2008.0093 opiate receptor gene dose effects on different morphine actions: evidence for Robledo, P., Berrendero, F., Ozaita, A., and Maldonado, R. (2008). Advances differential in vivo mu receptor reserve. Neuropsychopharmacology 25, 41–54. in the field of cannabinoid–opioid cross-talk. Addict. Biol. 13, 213–224. doi: doi: 10.1016/S0893-133X(00)00252-9 10.1111/j.1369-1600.2008.00107.x Stein, C. (2013). Opioids, sensory systems and chronic pain. Eur. J. Pharmacol. 716, Roques, B. P., Fournie-Zaluski, M. C., and Wurm, M. (2012). Inhibiting the break- 179–187. doi: 10.1016/j.ejphar.2013.01.076 down of endogenous opioids and cannabinoids to alleviate pain. Nat. Rev. Drug Steiner, H., Bonner, T. I., Zimmer, A. M., Kitai, S. T., and Zimmer, A. (1999). Discov. 11, 292–310. doi: 10.1038/nrd3673 Altered gene expression in striatal projection neurons in CB1 cannabinoid Rubinstein, M., Mogil, J. S., Japon, M., Chan, E. C., Allen, R. G., and Low, receptor knockout mice. Proc. Natl. Acad. Sci. U.S.A. 96, 5786–5790. doi: M. J. (1996). Absence of opioid stress-induced analgesia in mice lacking beta- 10.1073/pnas.96.10.5786 endorphin by site-directed mutagenesis. Proc. Natl. Acad. Sci. U.S.A. 93, Sun, X., Wang, H., Okabe, M., Mackie, K., Kingsley, P. J., Marnett, L. J., et al. (2009). 3995–4000. doi: 10.1073/pnas.93.9.3995 Genetic loss of faah compromises male fertility in mice. Biol. Reprod. 80, 235–242. Ruehle, S., Remmers, F., Romo-Parra, H., Massa, F., Wickert, M., Wortge, S., doi: 10.1095/biolreprod.108.072736 et al. (2013). Cannabinoid CB1 receptor in dorsal telencephalic glutamatergic Swendsen, J., and Le Moal, M. (2011). Individual vulnerability to addiction. Ann. neurons: distinctive sufficiency for hippocampus-dependent and amygdala- N. Y. Acad. Sci. 1216, 73–85. doi: 10.1111/j.1749-6632.2010.05894.x dependent synaptic and behavioral functions. J. Neurosci. 33, 10264–10277. doi: Szutorisz, H., Dinieri, J. A., Sweet, E., Egervari, G., Michaelides, M., Carter, 10.1523/JNEUROSCI.4171-12.2013 J. M., et al. (2014). Parental THC exposure leads to compulsive heroin- Sanchis-Segura, C., Cline, B. H., Marsicano, G., Lutz, B., and Spanagel, R. (2004). seeking and altered striatal synaptic plasticity in the subsequent generation. Reduced sensitivity to reward in CB1 knockout mice. Psychopharmacology (Berl) Neuropsychopharmacology 39, 1315–1323. doi: 10.1038/npp.2013.352 176, 223–232. doi: 10.1007/s00213-004-1877–1878 Tanimura, A., Yamazaki, M., Hashimotodani, Y., Uchigashima, M., Kawata, S., Abe, Sanchis-Segura, C., and Spanagel, R. (2006). Behavioural assessment of drug rein- M., et al. (2010). The endocannabinoid 2-arachidonoylglycerol produced by dia- forcement and addictive features in rodents: an overview. Addict. Biol. 11, 2–38. cylglycerol lipase alpha mediates retrograde suppression of synaptic transmission. doi: 10.1111/j.1369-1600.2006.00012.x Neuron 65, 320–327. doi: 10.1016/j.neuron.2010.01.021 Saunders, B. T., and Robinson, T. E. (2013). Individual variation in resisting temp- Taschler, U., Radner, F. P., Heier, C., Schreiber, R., Schweiger, M., Schoiswohl, tation: implications for addiction. Neurosci. Biobehav. Rev. 37, 1955–1975. doi: G., et al. (2011). Monoglyceride lipase deficiency in mice impairs lipolysis and 10.1016/j.neubiorev.2013.02.008 attenuates diet-induced insulin resistance. J. Biol. Chem. 286, 17467–17477. doi: Scavone, J. L., Sterling, R. C., and Van Bockstaele, E. J. (2013). Cannabinoid 10.1074/jbc.M110.215434 and opioid interactions: implications for opiate dependence and withdrawal. Tebano, M. T., Martire, A., and Popoli, P. (2012). Adenosine A(2A)-cannabinoid Neuroscience 248, 637–654. doi: 10.1016/j.neuroscience.2013.04.034 CB(1) receptor interaction: an integrative mechanism in striatal glutamater- Schlosburg, J. E., Blankman, J. L., Long, J. Z., Nomura, D. K., Pan, B., Kinsey, gic neurotransmission. Brain Res. 1476, 108–118. doi: 10.1016/j.brainres.2012. S. G., et al. (2010). Chronic monoacylglycerol lipase blockade causes functional 04.051 antagonism of the endocannabinoid system. Nat. Neurosci. 13, 1113–1119. doi: Tian, M., Broxmeyer, H. E., Fan, Y., Lai, Z., Zhang, S., Aronica, S., et al. 10.1038/nn.2616 (1997). Altered hematopoiesis, behavior, and sexual function in mu opioid Schuller,A. G., King, M.A., Zhang, J., Bolan, E., Pan,Y.X., Morgan, D. J., et al. (1999). receptor-deficient mice. J. Exp. Med. 185, 1517–1522. doi: 10.1084/jem.185. Retention of heroin and morphine-6 beta-glucuronide analgesia in a new line of 8.1517 mice lacking exon 1 of MOR-1. Nat. Neurosci. 2, 151–156. doi: 10.1038/5706 Tomasiewicz, H. C., Jacobs, M. M., Wilkinson, M. B., Wilson, S. P., Nestler, E. J., and Sharifi, N., Diehl, N., Yaswen, L., Brennan, M. B., and Hochgeschwender, U. (2001). Hurd, Y. L. (2012). Proenkephalin mediates the enduring effects of adolescent Generation of dynorphin knockout mice. Brain Res. Mol. Brain Res. 86, 70–75. cannabis exposure associated with adult opiate vulnerability. Biol. Psychiatry 72, doi: 10.1016/S0169-328X(00)00264-3 803–810. doi: 10.1016/j.biopsych.2012.04.026 Simonin, F., Befort, K., Gaveriaux-Ruff, C., Matthes, H., Nappey, V.,Lannes, B., et al. Trigo, J. M., Martin-Garcia, E., Berrendero, F., Robledo, P., and Maldonado, R. (1994). The human delta-opioid receptor: genomic organization, cDNA cloning, (2010). The endogenous opioid system: a common substrate in drug addic- functional expression, and distribution in human brain. Mol. Pharmacol. 46, tion. Drug Alcohol Depend. 108, 183–194. doi: 10.1016/j.drugalcdep.2009. 1015–1021. 10.011 Simonin, F., Gaveriaux-Ruff, C., Befort, K., Matthes, H., Lannes, B., Micheletti, Tsuboi, K., Okamoto, Y., Ikematsu, N., Inoue, M., Shimizu, Y., Uyama, T., et al. G., et al. (1995). kappa-Opioid receptor in humans: cDNA and genomic cloning, (2011). Enzymatic formation of N-acylethanolamines from N-acylethanolamine chromosomal assignment, functional expression, pharmacology, and expression plasmalogen through N-acylphosphatidylethanolamine-hydrolyzing phospholi- pattern in the central nervous system. Proc. Natl. Acad. Sci. U.S.A. 92, 7006–7010. pase D-dependent and -independent pathways. Biochim. Biophys. Acta 1811, doi: 10.1073/pnas.92.15.7006 565–577. doi: 10.1016/j.bbalip.2011.07.009

Frontiers in Pharmacology | Neuropharmacology February 2015 | Volume 6 | Article 6 | 14 Befort Opioid and cannabinoid systems interaction in reward

Tzschentke, T. M. (2007). Measuring reward with the conditioned place prefer- Xi, Z. X., Peng, X. Q., Li, X., Song, R., Zhang, H. Y., Liu, Q. R., et al. (2011). Brain ence (CPP) paradigm: update of the last decade. Addict. Biol. 12, 227–462. doi: cannabinoid CB(2) receptors modulate cocaine’s actions in mice. Nat. Neurosci. 10.1111/j.1369-1600.2007.00070.x 14, 1160–1166. doi: 10.1038/nn.2874 Uchigashima, M., Yamazaki, M., Yamasaki, M., Tanimura, A., Sakimura, Yaswen, L., Diehl, N., Brennan, M. B., and Hochgeschwender, U. (1999). Obesity K., Kano, M., et al. (2011). Molecular and morphological configura- in the mouse model of pro-opiomelanocortin deficiency responds to peripheral tion for 2-arachidonoylglycerol-mediated retrograde signaling at mossy cell- melanocortin. Nat. Med. 5, 1066–1070. doi: 10.1038/12506 granule cell synapses in the dentate gyrus. J. Neurosci. 31, 7700–7714. doi: Yoshino, H., Miyamae, T., Hansen, G., Zambrowicz, B., Flynn, M., Pedicord, D., et al. 10.1523/JNEUROSCI.5665-10.2011 (2011). Postsynaptic diacylglycerol lipase mediates retrograde endocannabinoid Uriguen, L., Berrendero, F., Ledent, C., Maldonado, R., and Manzanares, J. (2005). suppression of inhibition in mouse prefrontal cortex. J. Physiol. 589, 4857–4884. Kappa- and delta-opioid receptor functional activities are increased in the caudate doi: 10.1113/jphysiol.2011.212225 putamen of cannabinoid CB1 receptor knockout mice. Eur. J. Neurosci. 22, 2106– Zanettini, C., Panlilio, L. V., Alicki, M., Goldberg, S. R., Haller, J., and Yasar, 2110. doi: 10.1111/j.1460-9568.2005.04372.x S. (2011). Effects of endocannabinoid system modulation on cognitive and Valverde, O., Maldonado, R., Valjent, E., Zimmer, A. M., and Zimmer, A. (2000). emotional behavior. Front. Behav. Neurosci. 5:57. doi: 10.3389/fnbeh.2011.00057 Cannabinoid withdrawal syndrome is reduced in pre-proenkephalin knock-out Zhang, H. Y., Gao, M., Liu, Q. R., Bi, G. H., Li, X., Yang, H. J., et al. (2014). mice. J. Neurosci. 20, 9284–9289. Cannabinoid CB2 receptors modulate midbrain dopamine neuronal activity Valverde, O., and Torrens, M. (2012). CB1 receptor-deficient mice as a model and dopamine-related behavior in mice. Proc. Natl. Acad. Sci. U.S.A. doi: for depression. Neuroscience 204, 193–206. doi: 10.1016/j.neuroscience.2011. 10.1073/pnas.1413210111 09.031 Zhu, Y., King, M. A., Schuller, A. G., Nitsche, J. F., Reidl, M., Elde, R. P., et al. (1999). Van’t Veer, A., Bechtholt, A. J., Onvani, S., Potter, D., Wang, Y., Liu- Retention of supraspinal delta-like analgesia and loss of morphine tolerance in Chen, L. Y., et al. (2013). Ablation of kappa-opioid receptors from brain delta opioid receptor knockout mice. Neuron 24, 243–252. doi: 10.1016/S0896- dopamine neurons has anxiolytic-like effects and enhances cocaine-induced 6273(00)80836-3 plasticity. Neuropsychopharmacology 38, 1585–1597. doi: 10.1038/npp.2 Zimmer, A., Valjent, E., Konig, M., Zimmer, A. M., Robledo, P., Hahn, H., et al. 013.58 (2001). Absence of delta-9-tetrahydrocannabinol dysphoric effects in dynorphin- van Rijn, R. M., and Whistler, J. L. (2009). The delta(1) opioid receptor is a het- deficient mice. J. Neurosci. 21, 9499–9505. erodimer that opposes the actions of the delta(2) receptor on alcohol intake. Biol. Zimmer, A., Zimmer, A. M., Hohmann, A. G., Herkenham, M., and Bonner, Psychiatry 66, 777–784. doi: 10.1016/j.biopsych.2009.05.019 T. I. (1999). Increased mortality, hypoactivity, and hypoalgesia in cannabinoid Vigano, D., Rubino, T., and Parolaro, D. (2005). Molecular and cellular basis of CB1 receptor knockout mice. Proc. Natl. Acad. Sci. U.S.A. 96, 5780–5785. doi: cannabinoid and opioid interactions. Pharmacol. Biochem. Behav. 81, 360–368. 10.1073/pnas.96.10.5780 doi: 10.1016/j.pbb.2005.01.021 Vinod, K. Y., Sanguino, E., Yalamanchili, R., Manzanares, J., and Hungund, Conflict of Interest Statement: The author declares that the research was conducted B. L. (2008). Manipulation of fatty acid amide hydrolase functional activity in the absence of any commercial or financial relationships that could be construed alters sensitivity and dependence to ethanol. J. Neurochem. 104, 233–243. doi: as a potential conflict of interest. 10.1111/j.1471-4159.2007.04956.x Weibel, R., Reiss, D., Karchewski, L., Gardon, O., Matifas, A., Filliol, D., et al. (2013). Received: 07 November 2014; paper pending published: 27 November 2014; accepted: Mu opioid receptors on primary afferent nav1.8 neurons contribute to opiate- 08 January 2015; published online: 05 February 2015. induced analgesia: insight from conditional knockout mice. PLoS ONE 8:e74706. Citation: Befort K (2015) Interactions of the opioid and cannabinoid systems in reward: doi: 10.1371/journal.pone.0074706 Insights from knockout studies. Front. Pharmacol. 6:6. doi: 10.3389/fphar.2015.00006 Wise, L. E., Shelton, C. C., Cravatt, B. F., Martin, B. R., and Lichtman, A. H. (2007). This article was submitted to Neuropharmacology, a section of the journal Frontiers in Assessment of anandamide’s pharmacological effects in mice deficient of both Pharmacology. fatty acid amide hydrolase and cannabinoid CB1 receptors. Eur. J. Pharmacol. Copyright © 2015 Befort. This is an open-access article distributed under the terms of the 557, 44–48. doi: 10.1016/j.ejphar.2006.11.002 Creative Commons Attribution License (CC BY). The use, distribution or reproduction Wotherspoon, G., Fox, A., Mcintyre, P., Colley, S., Bevan, S., and Winter, in other forums is permitted, provided the original author(s) or licensor are credited J. (2005). Peripheral nerve injury induces cannabinoid receptor 2 pro- and that the original publication in this journal is cited, in accordance with accepted tein expression in rat sensory neurons. Neuroscience 135, 235–245. doi: academic practice. No use, distribution or reproduction is permitted which does not 10.1016/j.neuroscience.2005.06.009 comply with these terms.

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